RESULTS OF THE GERMAN AND AMERICAN SUBMARINE CAMPAIGNS OF WORLD WAR II

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Economic statecraft remains a relatively unstudied and misunderstood area of national security studies. David Baldwin's Economic Statecraft concludes that much of the American political establishment believes that any attempt to influence a rival nation's policies through application of economic pressure in peacetime will invariably fail.⁽¹⁾ He theorizes that most analysts underestimate the utility of economic statecraft; moreover, Baldwin infers that this underestimation exists primarily because so few analysts study economic statecraft.⁽²⁾

Economic warfare is a subset of economic statecraft. Economic warfare implies that one nation attempts to attack the industrial or logistical basis of an enemy's strength in order to shape a war's outcome. Examples of economic warfare include strategic bombing of an enemy's war industry, or cutting sea lines of communication to prevent the import of materials needed by an opponent's industry. Like economic statecraft, analysts neglect the study of economic warfare and typically misunderstand it's utility. Galbraith's well-known analysis of the U.S. World War II Strategic Bombing Campaign in Germany is a case in point. Galbraith concluded that the strategic bombing of Germany did not reduce industrial production.⁽³⁾ Roche and Watts clearly show that Galbraith reached a fallacious conclusion because he measured only direct military effects of the bombing campaign and did not account for important indirect and second order effects of the campaign on the German war effort.⁽⁴⁾

The economic effects of naval warfare on an enemy's ability to project power are also neglected and misunderstood. For example, the two great submarine campaigns of World War II are studied primarily for the military lessons learned; little analysis has been done on the logistical and economic effects of these campaigns. What analysis that has been done is often too simplistic. For example, Pugh's Cost of Seapower analyzes the German World War II submarine campaign from an economic basis and determines that the German campaign was not cost effective.⁽⁵⁾ Like Galbraith's analysis, however, Pugh does not account for appropriate indirect effects; moreover, he misses a substantial portion of the direct effects of the campaign.⁽⁶⁾

This paper will analyze the direct, indirect and second order effects of the German World War II Atlantic submarine campaign and the U.S. World War II Pacific submarine campaign.⁽⁷⁾ The successful U.S. campaign is relevant to the study of economic war because the campaign demonstrates how naval warfare can seriously impact an enemy's industrial war effort.⁽⁸⁾ The German campaign's relevance to economic warfare is subtler. Generally regarded as a failure, this campaign demonstrates how naval warfare that does not directly reduce industrial production can impose serious logistical constraints on an enemy. It is my thesis that the German and American led submarine campaigns were cost effective and imposed significant logistical constraints on their opponents.

Traditionally, naval forces seek to gain victory by defeating opposing naval forces, thereby allowing unfettered use of the seas to project power to distant areas of the world. The American theorist Alfred Thayer Mahan most effectively articulated the view that destruction of the enemy battle fleet was the precursor to effective control of the sea.⁽⁹⁾ The U.S., British and Japanese Navies all subscribed to the importance of Mahanian battle and therefore focused doctrinally on the destruction of the enemy battle fleet.⁽¹⁰⁾ This predisposition to force on force planning remains in the U.S. Navy today.

mahan downplayed the importance of the guerre de course, the concept of employing naval forces against an opposing merchant marine.⁽¹¹⁾ Navies too weak to directly attack opposing navies have employed the guerre de course as a way to deny use of the sea to their opponents with historically mixed results. However, war during the industrial age has increased the importance of sea lines of communications (SLOCs). Twentieth century armies based overseas require substantial maritime support in order to supply their immense logistical needs.⁽¹²⁾ Destroying or reducing the flow of the ships meeting these logistical needs constitutes an important vulnerability to the ability to project power overseas. Furthermore, some nations (including Japan), lack important natural resources, and must import enormous amounts of raw materials for industrial use. Interdiction of these resources by conducting attacks against sea lines of communications provides another means of reducing an enemy's ability to support modern warfare

U.S. planning today assumes that we will be able to effectively defend our flow of follow on forces with little thought as to how this will be done. Logistical planning is simply a matter of ensuring that the proper supplies are loaded on the right ships. The lessons learned from the campaigns we will study indicate that the United States should plan for the potential efforts of an adversary to attack American sea lines of communication in order to inhibit our ability to project power.

At the start of World War II, the German Navy was too small to directly challenge the English fleet for control of the sea. The only strategic possibility for the Germans was to attack allied commerce using their small submarine fleet. Throughout the war, the German Navy conducted a classic guerre de course, using aircraft, surface units and, above all, submarines to attempt to destroy allied commerce. Admiral Donitz's (head of the German submarine force) strategy employed his U-boats at the weakest point in enemy defenses where they could sink a maximum of tonnage.⁽¹³⁾ Donitz's goal, therefore, was to cut England's supply of war materiel and, later, to prevent American productive and military capability from influencing the European theater.

In six years of pitched battles throughout the Atlantic, German U-boats, often employing wolfpack tactics and night surface attacks, attempted to destroy opposing convoys. Throughout the war, Allied scientific and technical developments, along with improvements in tactical doctrine, competed fiercely against German technical and doctrinal development. In the end, the vast allied productive capability, which assured plentiful escorts and merchant ships, and superior tactics, weapons and sensors resulted in Allied victory. After May 1943, although they attempted several additional challenges to allied supply lines, the Germans never could truly contest Allied control of the sea.

During the war the Germans sank 5,150 allied ships displacing 21.57 million tons. Of this, the U-boats were responsible for 2828 ships of 14.69 million tons.⁽¹⁴⁾ To place this in perspective, the Germans sank the equivalent of the entire British merchant fleet at the start of the war.⁽¹⁵⁾ Additionally, submarines destroyed 187 warships, including 6 aircraft carriers and 2 battleships.⁽¹⁶⁾ However, this tremendous destruction came at a heavy price: the Germans lost 785 submarines of 1,158 constructed.

These losses and the loss of valuable cargo are the direct effects of the Battle of the Atlantic. In the end, however, the U-boats did not prevent the U.S. from supplying England with military and industrial goods or food, nor from building up U.S. forces in England (Operation Bolero), nor from providing Russia with substantial material help. Thus, most historians see the Battle of the Atlantic as a German failure.

There were, however, substantial indirect and second order effects on the allied war effort. These effects resulted in significant allied logistical constraints. For example, the indirect effects of convoying severely reduced allied transportation capacity. The Allies calculated that a ship took 18-48% longer to sail in convoy.⁽¹⁷⁾ Donitz estimated the loss of time at 33% on average.⁽¹⁸⁾ The impact on Army logistics and U.S. strategy was significant. In response to the German campaign, the U.S. ordered much greater quantities of munitions and supplies that was actually needed, in order to "fill the pipeline," to replace cargoes lost at sea and as a hedge against the Germans cutting the Atlantic supply lanes.⁽¹⁹⁾

The result of this "loss of time" combined with significant losses (up until July 1943, Allied merchant ship losses exceeded production) had two effects on the Allied war effort. First, the Allies needed to produce and ship more war material than was actually required in theater. Secondly, the Allies possessed less logistical carrying capacity than desired. As a result of the lack of merchant shipping and material, the U.S. Army significantly reduced the size of their planned buildup to far more modest proportions (the original intention in 1942 was to build a large army of 16-17 million men).⁽²⁰⁾ Although speculative, it is probable that such a reduction meant that the combined U.S. and British Armies would have been incapable of defeating the Wehrmacht without the sizeable Red Army in the war.⁽²¹⁾

The U-boat attack on allied supply lines had a pronounced second order effect on allied production priorities. Throughout the war, the Allies had to prioritize between warship, merchant and amphibious production (as well as other uses for steel). In the fall of 1942, the Allies increased amphibious shipping to their highest production priority in a crash program to prepare for Roundup (the planned 1943 cross channel invasion).⁽²²⁾ Yet this buildup came at a difficult time when the Navy was 'straining' to replace the losses from Pearl Harbor, construct a battle fleet to win back dominance of the Pacific and build sufficient escorts and merchants to prevail against the potent German U-boat offensive."⁽²³⁾

By the winter of 1942-43, the Allies cut back the landing craft program and increased escort production in order to counter renewed losses to German U-boats.⁽²⁴⁾ Hall concurs, noting that landing craft production was removed from FDR's "must" (highest priority for war production) program comprising rubber, high octane fuel, aircraft, escort vessels, and merchant shipping and pointing out that the change in priority was due to the need to increase escort production.⁽²⁵⁾ Landing craft production fell off from 105,000 tons in Feb 1943 to 51,000 tons in July 1943.⁽²⁶⁾

The Allies' lack of landing craft would logistically constrain allied forces for the rest of the war. General George Marshall noted a "shortage which would plague us to the final day of the war in Europe-the shortage of assault craft, LSTs, LCIs and smaller vessels. This he described as the greatest by far of all the problems."⁽²⁷⁾ The British official review analyzed the situation in a similar way:

"In so far as the delays in launching the offensive could be attributed to an insufficient supply of landing craft, they were in the last resort due to the high strategic and industrial priority which the Allied leaders assigned to the defense of the shipping lanes."⁽²⁸⁾

To get full measure of the effects of the Battle of the Atlantic on Allied strategy, we must look at the combined effects of inadequate numbers of landing craft and inadequacy of logistical means due to heavy losses of merchant ships. Hall notes that:

Heavy shipping losses and the resulting lack of logistical capacity played a prominent role in ruling out a 1943 invasion of France. Experts calculated only 8 U.S. divisions could be transported to Europe (11 without convoy restrictions) by the spring of 1943. Even if the invasion was delayed till September, U.S. forces would number only 12 divisions- which combined with 13 British divisions would be badly outnumbered by the 44 German divisions stationed in the West.⁽³⁰⁾

With a cross channel invasion out of the question for 1943, the Allies embarked on a major effort in the Mediterranean - yet logistical constraints and landing craft limitations played a key and limiting role in the formulation of strategy throughout the southern theater. For example, concern over the line of communications played a deciding role in limiting the Allied attack on North Africa to the west of that continent rather than an early allied lodgment in Tunisia.⁽³¹⁾ Additionally, at the Casablanca conference, logistical constraints and security of shipping was the key consideration in the selection of Sicily rather than Sardinia as the next target for Allied attack, and in the strong American opposition to more ambitious undertakings against Italy or in the eastern Mediterreanean.⁽³²⁾

During the fall of 1943, allied victory in the Battle of the Atlantic resulted in another change of allied war production priorities. Allied leaders pared back escort production and again increased the priority of amphibious assault shipping.⁽³³⁾ The change came too late to prevent serious restrictions on Allied strategy and the feasibility of operations throughout 1944. Lack of assault and merchant shipping continued to plague Allied planners and resulted in heated discussions at the Cairo and Tehran conferences of late 1943 regarding what operations would be pursued. Lack of lift resulted in abandonment of operations in the Eastern Mediterranean.⁽³⁴⁾ Despite FDR's promise to Chiang Kai-shek, the Allies cancelled amphibious assaults planned against Japanese forces in Burma.⁽³⁵⁾ Lack of assault shipping and the desire to maintain an attack up the Italian peninsula towards Rome, resulted in the Allies postponing the Overlord invasion by more than one month.⁽³⁶⁾ Of greater import, the same lack of assault shipping resulted in postponement of the invasion of Southern France (Anvil). Originally designed to draw mobile German forces away from Normandy, Anvil as executed in August was "disconnected strategically" from Overlord and served little utility.⁽³⁷⁾

Logistical constraints, attributable to the Battle of the Atlantic, resulted in two interesting "what-ifs" affecting the allied effort in Northern France. First, divisions sent into the Mediterranean Theater were "irrevocably bound there for lack of shipping to deploy them elsewhere."⁽³⁸⁾ While these Allied divisions tied down German troops in Italy, they were unavailable to exploit or reinforce Allied efforts in Northern France, a theater, by the way, which was much more suitable for offensive operations and logistical support. Secondly, had U-boat successes continued for several months longer in 1943 the Allies might have been incapable of a cross channel invasion in 1944. British imports fell to lower than sustainable levels early in 1943, resulting in a request for the U.S. to turn over a large amount of shipping to provide for British import needs. Despite warnings that the total American lift to England and the Mediterranean in 1943 could fall from 1.5 million to 800,000 men, FDR approved the transfer of transports. Only the sudden and unexpected defeat of the U-boats provided a respite for the Allies-and allowed the transports to England to buildup adequate forces for a Cross Channel invasion in 1944.⁽³⁹⁾

The U-boat guerre de course clearly imposed logistical constraints on the Allies and limited their strategic freedom of action. Indeed, one can argue that the Battle of the Atlantic may have delayed the conclusion of the war.

Morrison stated that the Allies spent "hundreds of billions of dollars" to defeat the U-boat.⁽⁴⁰⁾ Donitz noted that he kept his U-boats in the Atlantic after their defeat in order to prevent the Allies from using their freed resources in other ways against Germany.⁽⁴¹⁾ To a casual observer, the Allies apparently employed disproportionate resources in defeating the U-boat menace. In order to understand better the magnitude of the effort the Allies placed in defeating the U-boat threat, the approximate costs of each side's efforts has been calculated.⁽⁴²⁾ For the Allies, these costs measure some, but not all, direct, indirect and second order costs. In general, the actual cost to the Allies has been underestimated (as will be seen). Three costs were analyzed:

1) Cost of ships destroyed by U-boats, plus the indirect costs associated with the loss of time in convoy (I have assumed 33% of the merchant fleet was thus rendered "ineffective").⁽⁴³⁾

2) The cost of ASW escorts and aircraft (this takes into account both direct costs (losses) plus second order costs). Only the cost of aircraft directly associated with ASW was calculated- coastal defense aircraft were not estimated, therefore, aircraft costs have been underestimated. Where prices could not be found (some British ships), I have based the price on an equivalent U.S. ship.⁽⁴⁴⁾

3) U-boat costs where based on the reported German costs (in Marks) with a wartime conversion factor applied (see Appendix 1). The costs accord fairly well with costs for U.S. submarines when adjusted for differences in construction man-hours.

Appendix 1 specifies how the costs were calculated. As a result, I have estimated that the Allies spent nearly 10 times what the Germans spent on their U-boat fleet. One should note that German submarine industry employed between 30,000 and 45,000 workers.⁽⁴⁵⁾ However, the Americans alone employed 640,000 workers at peak just to construct merchant ships during the war.⁽⁴⁶⁾ Thus, my calculation probably substantially underestimates the Allied effort during the war.

In 1937, the combined American and British national revenue was 275% that of Germany. Taking into account Russian national revenue (but not counting countries occupied by Germany), the total allied productive capacity was about 4 times that of Germany.⁽⁴⁷⁾ If one assumes that this relative inferiority of productive capability did not change substantially during the war, the Germans still chose a relatively "efficient" cost imposing strategy against the Allies. Another words, the Germans forced the Allies to dispense disproportionate costs in order to maintain control of the sea- resources that the Allies could have used in other ways to better effect.

The disproportionate costs and logistical constraints imposed on the Allies leads one to question the verdict of history that the campaign was a "failure" for Germany. While ultimately, German submariners did not win a decisive victory in the Atlantic, these iron warriors clearly gained time for the German war machine- an extraordinary feat considering that Germany started the war with just 57 submarines and eventually fought the world's two biggest navies combined. The German clearly waged an effective guerre de course. However, the results of the German submarine campaign would pale in comparison to the U.S. effort.

The Japanese attack on Pearl Harbor resulted in a significant loss of strength for the U.S. Navy and placed that Navy in a defensive posture. The only weapon system immediately available to take the war to the enemy was the U.S. submarine force. Indeed, FDR had decided prior to the start of the war that "unrestricted submarine warfare" would be undertaken in the event of hostilities with Japan.⁽⁴⁸⁾ Throughout the war, the growing U.S. submarine force was employed in attacks on Japanese merchant shipping as well as on Japanese fleet units when the opportunity presented itself. In both these tasks, the American submarine force was aided by magic- intelligence derived from broken Japanese codes.⁽⁴⁹⁾ The Japanese Navy, with Mahanian intellectual roots, prepared tardily and insufficiently for an onslaught not directly related to "decisive battle." The American Navy won a spectacular victory.

The Japanese Merchant Marine lost 8.1 million tons of vessels during the war, with submarines accounting for 4.9 million tons (60%) of the losses.⁽⁵⁰⁾ Additionally, U.S. submarines sank 700,000 tons of naval ships (about 30% of the total lost) including 8 aircraft carriers, 1 battleship and 11 cruisers.⁽⁵¹⁾ Of the total 288 U.S. submarines deployed throughout the war (including in the Atlantic), 52 submarines were lost with 48 destroyed in the war zones of the Pacific.⁽⁵²⁾ American submariners suffered the highest loss rate in the U.S. Armed Forces, with 22% killed. Of note, the personnel of the U.S. Submarine Force comprised only 1.6% of the American Navy.⁽⁵³⁾

The American Pacific submarine campaign had substantial direct, indirect and second-order effects on the Japanese economy and the four bases of Japanese military power- Japanese airpower, the Army, the Imperial Japanese Navy and the merchant marine. We will analyze the effects of the American guerre de course in each of these areas. It is important to note, just as in the Battle of the Atlantic, that the submarine was the predominant, but not the only, factor in the destruction of Japanese commerce and the ensuing damage to the Japanese economy. We cannot realistically look at the submarine campaign in complete isolation from other attacks against the Japanese transportation system.

The Japanese merchant marine started the war with 6 million tons of shipping. The Japanese Army and Navy each requisitioned a part of the merchant marine to transport and supply their respective operating forces. The Japanese leadership believed they needed to retain 3 million tons of shipping in order to meet the industrial and civilian needs of the economy- although this estimate was probably too low.⁽⁵⁴⁾ Two important points need to be made in order to understand the effect of the war on the Japanese transportation system. First, Japan's industrial capacity was proportional to her ability to import needed material.⁽⁵⁵⁾ Secondly, due to the extensive drafting of merchant vessels for military needs as well as high losses from American attacks, Japan never achieved the minimum of 3 million tons of capacity required for industrial and civilian uses.⁽⁵⁶⁾

Losses of merchant vessels combined with the indirect loss of a portion of the merchant marine fleet due to convoying significantly reduced Japanese economic strength. Imports of 16 key materials fell from 20 million tons in 1941 to 10 million tons in 1944 and 2.7 million tons in the first 6 months of 1945.⁽⁵⁷⁾ The specifics were impressive:

"Bauxite imports fell off 88% just between the summer and fall of 1944. In 1945, pig iron imports plunged 89%, pulp 90%, raw cotton and wool 91%, fats and oils 92%, iron ore 95%, soda and cement 96%, lumber 98%, fodder 99%, and not one ounce of sugar or raw rubber reached Japan."⁽⁵⁸⁾

Moreover, the reduction in imports of raw materials mirrored problems importing food. During 1944, average caloric intake fell 12% below the minimum daily requirement for the non-farming population.⁽⁵⁹⁾ The enormous drop in importation of raw materials resulted in a significant drop in Japanese industrial production. In fact, the Japanese mobilization committee stated in a late 1944 report: "Shipping lost or damaged since the beginning of the war amounts to two and one half times newly constructed shipping and formed the chief cause of the constant impoverishment of national strength."⁽⁶⁰⁾

Submarine attacks on the oil flow to Japan were a second critical factor in destroying Japanese military potential. Japanese oil imports fell from 1.75 million barrels per month in August 1943 to 360,000 barrels per month in July 1944. In October 1944, imports fell even more due to high losses around the Philippine battlefields.⁽⁶¹⁾ After September 1943, the ratio of petroleum successfully shipped from the southern regions that reached Japan never exceeded 28%, and during the last 15 months of the war the ratio only averaged 9%.⁽⁶²⁾ The losses are especially impressive when one considers that the Japanese Navy alone required 1.6 million barrels monthly to operate.⁽⁶³⁾ Much anecdotal evidence describes Japan's often desperate responses to the American guerre de course. For example, in early 1945, the Japanese Navy loaded crude oil barrels on battleships to import home, while at the same time the nation experimented with producing gasoline from potatoes.⁽⁶⁴⁾

The loss of raw materials and petroleum and inability to transport items to the front lines lay at the heart of Japan's weakening ability to maintain effective military strength. Munitions Minister Toyoda said as much when interrogated after the war: "the shipping shortage and the scarcity of oil were the two main factors that assumed utmost importance in Japan's war efforts."⁽⁶⁵⁾ We will now look at the specific effects of the drop in industrial production and inability to transport goods on Japanese airpower, naval and merchant marine shipbuilding and the army.

Aircraft production was strongly affected by the war against Japanese sea lines of communication (SLOCs) due to the lack of raw materials. By April 1944, aircraft engine production had fallen to "critical" levels.⁽⁶⁶⁾ The Japanese significantly reduced aircraft engine testing due to lack of aviation gas: from about 8 hours and 5 flights for each engine in 1941 to 2 hours of testing on 10% of the engines built at war's end.⁽⁶⁷⁾ The reduction of bauxite imports by 500,000 tons from Indonesia and Malaysia resulted in a 70% drop in aluminum production in 1944.⁽⁶⁸⁾ As a result, by the end of 1944, 80% of every plane was made from aluminum pilings which significantly reduced aircraft quality.⁽⁶⁹⁾ By the spring of 1945, the Japanese fabricated major parts of aircraft from wood and they actively planned to construct entire aircraft out of wood.⁽⁷⁰⁾

The war against Japanese SLOCs resulted in significant indirect effects on Japanese air strength. In fact, the reduction in Japan's air power strength was not so much due to the reduction of aircraft quality or production but due to the reduction in pilot quality. Fuel shortages substantially reduced pilot training.⁽⁷¹⁾ In 1944, the great Japanese naval aviator Fuchida complained about the "inadequate training" aviators received prior to attachment to an operational unit.⁽⁷²⁾ Moreover, once Japanese pilots reached operational units, their training opportunities often did not improve. For example, prior to the Battle of the Philippine Sea, Admiral Toyoda stationed his carriers at Tawitawi near the Borneo oil supplies due to the effective submarine campaign against Japanese tankers. U.S. commanders vectored submarines into the area. Alerted to the danger, the Japanese commander refused to sortie for training- with the result that what little skills his undertrained pilots possessed atrophied.⁽⁷³⁾ The resulting Japanese aerial defeat became known as the Marinas Turkey Shoot.

An additional indirect effect of the war against Japanese transportation should be noted. Inadequate numbers of merchants and fear of additional losses resulted in the use of barges and small boats to ferry supplies in the empire's combat zones. As a consequence, the Japanese undersupplied forward-deployed units, including ground based aviation units. As an example, one air staff officer noted "a 75% drop in aircraft serviceability in New Guinea from such causes [loss of shipping] and blamed the loss of aerial supremacy over that strategic island on transport shortages."⁽⁷⁴⁾

The submarine offensive gravely weakened a second pillar of Japanese power: the Imperial Japanese Navy (IJN). As previously discussed, 30% of total Japanese Navy losses were caused by U.S. submarines. Submarines played another important role in reducing IJN capabilities. Damage to ships, caused in part by submarines, significantly increased ship repair time in Japanese shipyards, thereby reducing opportunities for new construction. The Japanese Navy spent 12% of its construction budget on ship repairs in 1943 and 1944; the figure increased to 34% in 1945.⁽⁷⁵⁾ Additionally, the submarine campaign had two important second order effects on the Japanese Navy. First, the necessity to build merchant ships to replace losses resulted in a reduction of potential naval construction. Private shipyards devoted to naval construction fell from 44% of the total in 1942 to 30% in 1943.⁽⁷⁶⁾ Secondly, the requirement to build escort ships and naval transports (also to replace merchant losses) reduced the potential to build more powerful combatants. As a result, while the IJN used 14% of its construction budget for escorts and transports in 1941, the percentage shot up to 54.3% in 1944.⁽⁷⁷⁾ More astonishing, the need for escorts and merchants was so grave, that after 1943, the Japanese Navy started construction on no ship bigger than a destroyer!⁽⁷⁸⁾ Finally, the American stranglehold on imports, in this case, iron ore, proved fatal to any long term ability to build adequate numbers of warships to replace losses.⁽⁷⁹⁾ By September 1944, the Japanese had so little steel that naval construction fell precipitously.⁽⁸⁰⁾

We have examined the direct effects of the American submarine offensive against the Japanese merchant marine. The Japanese suffered an important indirect effect of submarine warfare caused by the loss of efficiency due to convoying. The entire merchant marine (including that shipping throughout the empire that was not convoyed) had a loss of efficiency of 8% between January 1942 and January 1944 with a further reduction of 21% by 1945.⁽⁸¹⁾ However, on the critical line between Singapore and Japan, efficiency declined by 45% between May 1943 and May 1944, with further substantial declines later.⁽⁸²⁾ Not only did Japan have too few ships, but their ships took longer and longer throughout the war to carry badly needed cargoes the same distances.⁽⁸³⁾

In response to American attacks, the Japanese attempted to increase construction of merchants to replace losses. The Japanese used 7% of their total steel production on merchants in 1941 but 46% in 1945.⁽⁸⁴⁾ Despite their best efforts, the import crisis hit merchant construction hard. Of note, concentrated submarine attacks on tankers resulted in the Japanese augmenting construction of the vital petroleum carriers at the expense of general-purpose ships. In the fall of 1944, lack of steel forced significant cutbacks on production.⁽⁸⁵⁾ Despite considerable efforts, Japan never succeeded in building more than 45% of her losses. In the words of the Strategic Bombing Study, the Japanese "didn't have the production potential to surpass wartime shipping losses."⁽⁸⁶⁾ The inability to protect merchants and replace losses could only result in disaster for such a nation so dependent on imports for survival.

The breakdown of the Japanese merchant marine placed grievous logistical constraints on the ability of the Japanese Empire to supply her army deployed throughout the Central and Southern Pacific. Japanese logistical problems first became apparent in 1942 during the Guadalcanal campaign, when an overstrained logistical system and relentless U.S. air attacks resulted in frontline Japanese units receiving only 10% of the supplies comparable American units received.⁽⁸⁷⁾ U.S. submarines attacks directly affected the ability of the Japanese to move troops and supplies into important combat zones. For example, concentrated submarine attacks on shipping delivering the experienced 32^nd and 35^th Infantry divisions to the New Guinea theater resulted in the Japanese convoy disembarking the surviving troops over 500 miles from their destination. As a consequence, the Japanese barged ineffectual penny packets of troops to combat McArthur's forces in Biak and Hollandia.⁽⁸⁸⁾ In another case, U.S. submarines destroyed 6 transports loaded with troops destined to boost the defenses of the Marinas before the U.S. invasion of those islands, and sank ships loaded with vital concrete and wire needed for the islands' fortification.⁽⁸⁹⁾ The rate of successful delivery of military supplies to front line units averaged 96% in 1942, declining to 83% in 1943, 67% in 1944 and 51% in 1945.⁽⁹⁰⁾ These statistics fail to capture the extraordinary indirect effects of both U.S. submarine and air attacks on Japanese merchants as the Japanese had to resort to carrying much of their supplies within the combat zones by slow, inefficient means such as barges, fishing boats and the like. These direct and indirect effects of U.S. attacks clearly impacted Japanese army units. Throughout the war, munitions deliveries were 15% below front line needs, and 33 to 50% of all food sent to the front was lost due to attack or spoilage.⁽⁹¹⁾ Accounts from front line units depict significant efforts to make up for lack of food deliveries by gardening, fishing, or bartering with natives with sporadic accounts of cannibalism in especially poorly supplied areas like New Guinea.⁽⁹²⁾

Several important second order and indirect effects must be noted in the U.S. submarine campaign. First, the Japanese used a portion of their submarine force to supply bypassed units. Indeed, the Japanese army and navy each built significant numbers of submarines designed for the express purpose of carrying cargo.⁽⁹³⁾ Not only were scarce resources wasted in this way, but Japanese submarines that could have been used to attack the extended American logistics train were not properly employed. Another important combined direct and indirect effect of the U.S. campaign against the Emperor's lines of communication was strategic immobility. The inadequacy of total lift and reliance on barges in theater meant large number of Japanese troops could not be quickly moved around the empire. U.S. sea and airpower usually prevented the Japanese from reinforcing islands under attack or removing defeated troops from an island under assault. Therefore, the Japanese could not exploit their advantage of interior lines of communication to move and supply adequate numbers of troops to defeat any of the three major Allied lines of advance in the Pacific theater.

As with the German campaign in the Atlantic, I have attempted to roughly calculate costs of each side's effort in order to determine whether the U.S. campaign was efficient.⁽⁹⁴⁾ However, unlike the allied convoying effort, which was uniformly conducted throughout the war with easily identified escort forces; the Japanese forces assigned to protect convoys are much harder to identify. The following guidelines were used to assign costs (see Appendix 2 for details):

1. Cost of ships destroyed by U.S. submarines, plus the indirect costs associated with the loss of time in convoy are included (I have assumed only 10% of the merchant fleet was thus rendered "ineffective" because not all ships were convoyed- but this is probably an underestimate).⁽⁹⁵⁾

2. The cost of Japanese naval ships sank by subs (using actual Japanese prices) and costs of all constructed ASW frigates and corvettes were included. Cost of ASW aircraft and part time use of fleet destroyers was not taken into account. Note, therefore, indirect costs are underestimated.

3. All 288 subs (regardless of where they served) are counted in U.S. submarine costs.

Based on this rough estimate, the Japanese spent at least 42 times more on Anti- Submarine Warfare and in losses attributed to submarines than the U.S. spent on her Submarine Force. When one considers the fact that the Japanese economy was only 8.9% of the size of the U.S. economy in 1937, the submarine campaign was clearly an extraordinarily cost efficient means to employ U.S. forces against Japan.⁽⁹⁶⁾

We have examined the direct, indirect and second-order effects of the U.S. submarine campaign against Japanese raw material and petroleum imports as well as the effects on four pillars of Japanese power. Fully a year before the end of the war, and before the extensive bombing of mainland Japan, the war against Japanese lines of communication resulted in decisive impact on the Japanese war economy and on the Japanese military logistical system.

We can draw several important lessons on the effectiveness of submarines attacking sea lines of communication based on our study of the two World War II historical cases. First, both these campaigns were directed against vulnerable opponents who required the use of the sea both to import raw materials and to project military forces far from the homeland. A submarine attack on seagoing logistical lines of communication would obviously not be effective against an insular, continental power. Second, both campaigns, including the "failed" German effort, incurred disproportionate costs on the side conducting Anti-Submarine Warfare (ASW). Third, the indirect and second order effects of these campaigns were virtually as important as the direct costs. In fact, the continuing indirect and second order effects played a key role in logistically constraining the Allies in the Atlantic after the allied defeat of the U-boat threat. Finally, in both campaigns, the effects of submarine warfare on an opponent resulted in a substantial reduction of the opponent's strategic choice and had significant effects on his industrial policy. In the case of the Atlantic campaign, the Allies modified industrial priorities and reduced production of amphibious lift. Lack of logistical and amphibious lift resulted in constrained allied strategic choice for most of the war including a delayed ability to open a second front in France. In the case of Japan, the U.S. submarine campaign substantially reduced Japanese war production, and, ultimately, significantly reduced the Japanese ability to implement their preferred defensive strategy. As a result, the submarine campaign proved itself as an efficient way to wage war against a competitor that must supply its forces over long distances by sea.

It is interesting to contemplate to what degree the United States is vulnerable today to a campaign by a committed regional power or peer competitor against our sea lines of communications. Within the U.S. Navy today, one hears some discussion on the possible impact of submarine attacks against our battle groups, but few consider the impact a campaign against our vulnerable sealift train might have. Since America remains dependent today on sealift to project military power, an opponent might well assess this vulnerability worth exploiting.

The analysis conducted above leads one to question the need for more careful and extensive study of issues relating to economic warfare and statecraft. This avenue of national security studies remains understudied and misunderstood, but it should not remain so. The submarine campaigns of World War II demonstrate that the ability to sever or attack industrial output or prevent supply to deployed forces can markedly change the conduct of a war.

1. Cost of merchant ships lost to sub attack: 14,687,231 tons lost at $420 a ton.⁽⁹⁷⁾

2. It is assumed that 50% of destroyed ships had cargoes and I have estimated the value of each cargo as equivalent to the price of the ship.⁽⁹⁸⁾

3. American Maritime Commission constructed 5,777 ships of 39,920,000 tons during the war that cost $14.2 billion.⁽⁹⁹⁾ It is estimated that only 2/3 were used in the Atlantic (this accords well with 61% reported in Leighton's Global Logistics 1940-43 (p.662) which was prior to the increase in lift necessary to handle Overlord).

4. The English and Canadians produced 11.9 million tons during the war.⁽¹⁰⁰⁾ It is assumed their cost of production was as low as in the U.S.⁽¹⁰¹⁾

5. The English started the war with 17,430,000 tons. The Americans started with 8.5 million tons (again only assumed 2/3 used in Atlantic). Additionally the Allies seized 3 million tons of shipping from nations occupied by the Axis.⁽¹⁰²⁾

6. It is assumed that 33% of the total merchant fleet was lost due to inefficiency of convoying. That is 11.36 million tons at $420/ton.⁽¹⁰³⁾

1. The Americans had 140 destroyers stationed in the Atlantic. Each cost approximately $10 million. Additionally, they had 56 frigates assigned to the Coast Guard. I've estimated their cost as similar to a new frigate ($2.3 million).⁽¹⁰⁴⁾

2. During the war, the U.S. produced 520 destroyer escorts (DDE) and 96 frigates (FF) for convoy protection. A DDE cost $5.5 million and a FF cost $2.3 million apiece.⁽¹⁰⁵⁾

3. The Allies built 61 escort carriers that participated in the campaign at a cost of $12 million a piece.⁽¹⁰⁶⁾

4. The English and Canadians built or seized 169 DDEs. I've estimated their costs as equivalent to a Hunt class DDE ($6.4 million).⁽¹⁰⁷⁾ They also built 156 frigates, 63 sloops (estimated to cost $4 million), 306 Corvettes, 27 other ASW vessels, and 15 armed merchant cruisers (all estimated at $3 million).⁽¹⁰⁸⁾

5. The English employed about 302 fleet destroyers during the war.⁽¹⁰⁹⁾ I've estimated that only 50% of their missions were related to ASW and that they cost the equivalent of an U.S. destroyer (a probable underestimation).⁽¹¹⁰⁾

6. The cost of coastal defense craft and minesweepers used for ASW missions was not estimated.

1. 2828 U.S. patrol aircraft were used in the Atlantic.⁽¹¹¹⁾ I've used either exact prices as given by Holley, or the cost of similar aircraft.⁽¹¹²⁾

2. The U.S. used 4719 tactical aircraft in the Atlantic fleet. I've assumed that 50% of their missions were related to ASW.⁽¹¹³⁾

3. No costs of the U.S. Army Air Corps or of the Civil Air Patrol (both limited participants in the campaign) were included.

4. I've used the number of English and Canadian squadrons and CVEs (i.e. 24 aircraft per CVE) to estimate total numbers of aircraft.⁽¹¹⁴⁾ I doubled the numbers to account for losses etc. The total was 740 patrol aircraft and 850 tactical aircraft. This is probably an underestimation when one considers U.S. aircraft numbers.

5. The Allies lost at least 200 heavy bombers in attacks on against U-boat bases or production facilities.

6. To the extent that air operations tend to be expensive relative to the cost of operating ships, allied costs are probably significantly underestimated.

1. German data was used to determine the cost of submarines.⁽¹¹⁵⁾ Where cost data on specific types of submarines could not be found (Type XIV, XXIII, Walther), I estimated the price based upon German submarines of similar displacement, accounting for differences in construction man-hours. The exchange rate was based upon wartime U.S. estimates (I used $.50 per mark, the 1942 estimate).⁽¹¹⁶⁾ Of note, the cost of a U.S. submarine in 1943 was about $3 million.⁽¹¹⁷⁾ The figures for German submarines are reasonable when compared to U.S. costs and man-hours required for construction.⁽¹¹⁸⁾

10. Only the costs of the 1,158 submarines completely constructed were calculated.

Conclusion: The Allies total investment was $26.4 billion compared to the German investment of $2.76 billion. The Allies spent at least 9.6 times the German investment.

Tonnage of Japanese Warships sunk by submarines as indicated by JANAC. The costs of all Japanese ships are as listed in U.S. Strategic Bombing Survey.

9. The costs of destroyers and aircraft as well as a variety of small craft used in the ASW role have not been calculated.

1. 5,121,000 tons sank or probably sank by submarines. According to the Japanese, the average cost of a merchant was 864 Yen/ton.

2. It is estimated that 50% of all ships sank were loaded with cargo and that the cargo was valued at the same price as the ship.⁽¹¹⁹⁾

3. It is estimated that 10% of the fleet of 6 million tons was lost due to the inefficiency of convoying.⁽¹²⁰⁾

C. Conversion Estimate: Conversion costs are difficult to assess. The cost of a destroyer (since they were relatively similar in both navies) is used to compare. The U.S. paid $6400/ton, the Japanese paid 3522 Yen/ton or about $1000/ton at prewar exchange rates. If one estimates both countries as having equal efficiency, one must multiply the Japanese costs by 6.4. However, according to the U.S. Bombing Survey, Japanese shipyards were significantly less efficient. Japanese costs have been multiplied by 2 (which accords well with length of time to complete equivalent ships) in order to account for this variation in shipyard efficiency for a total multiplication of 12.8.⁽¹²¹⁾ This efficiency factor is conservative. During the war, the Americans estimated that Japanese worker efficiency (based upon prewar industrial data), was 29% that of the U.S.worker.⁽¹²²⁾

2. 3 R-class plus Barracuda, Bass and Bonita (returned from mothballs)- $.85 Million per ship.

¹ D.A. Baldwin, Economic Statecraft, (Princeton, Princeton University Press, 1985), pp.3-4, 372-3.

³ J.G Roche and B.D Watts, "Choosing Analytic Measures," The Journal of Strategic Studies, (June 1991), pp. 175-6.

⁴ Ibid., pp. 176-7. Direct costs involve actual damage inflicted on an enemy (reduction in production due to bombing); indirect costs are costs associated with a byproduct of the action (reduction in production due to dispersal of enemy factories); second order costs are associated with long term response to the action (reduced production of needed hardware in order to produce more fighters).

⁵ P. Pugh, The Cost of Seapower, (London, Conway Maritime Press, 1986), pp. 240-6.

⁶ Pugh counts only the cost of English and Canadian destroyer production and compares them to U-boat construction costs. Direct costs of merchants, U.S. ship and allied aircraft production costs are not analyzed. No attempt is made to investigate key indirect and second order effects.

⁷ Examples of submarine induced direct costs is loss of enemy merchants or warships; example of indirect costs are loss of part of the effective merchant fleet due to convoying; example of second order costs is the cost of additional escorts built to combat submarines.

⁸ We will also examine the affect of the U.S. submarine campaign on the Japanese ability to logistically supply their forces.

⁹ E.B. Potter, Sea Power: A Naval History (Annapolis, U.S. Naval Institute Press, 1989), p. 162.

¹⁰ The Japanese, for example, translated and published more works of Mahan than any other country.

Mark Parillo, "The Imperial Japanese Navy in World War II," Reevaluating Major Naval Combatants of World War II. (New York, Greenwood Press, 1990), p. 70.

¹² U.S. forces received 94.4 % of their supplies from sea during the Persian Gulf War. United States Transportation Command, So Much, So Far, So Fast. (Washington, D.C., U.S. Government Printing Office, 1996), p. 17.

¹⁴ R.A. Bowling, The Negative Influence of Mahan on on the Protection of Shipping in Wartime (University of Maine, 1980), p. 664.

¹⁶16 S.W. Roskill, The War at Sea, 1939-1945 (London, H.M. Majesty's Office, 1954), Vol. 3, pp. 339-447.

¹⁷ Chief of Naval Operations, Shipping in Naval Logistics (Washington D.C., Navy Department, 1945), p. 104.

¹⁹ Richard. M. Leighton and Robert W. Oakley, Global Logistics and Strategy, 1940-43 (Washington, D.C., Center of Military History, 1995), p. 15.

²⁰ H. D. Hall, North American Supply (London, H.M. Majesty's Stationery Office, 1955), p. 397.

Maurice Matloff, "The 90 Division Gamble", Command Decisions, (Washington, D.C., U.S. Government Printing Office, 1960), p. 368.

K.G. Greenfield, R.R. Palmer and B.I. Wiley, The Organization of Ground Combat Troops, U.S. Army in World War II, (Washington, D.C., U.S. Government Printing Office, 1947), pp.214-5.

²² Richard M. Leighton, Command Decision: Overlord vs. the Mediterranean at the Cairo-Tehran Conferences (Washington, D.C., Center of Military History, 1990), pp. 259-260.

²⁸ M.M. Postan, British War Production (London, H.M. Stationery Office, 1952), p. 292.

³⁹ R.M. Leighton, Command Decisions: U.S. Merchant Shipping and the British Import Crisis (Washington, D.C., Center of Military History, 1990), pp. 201-214. The reduction in troop numbers would have fulfilled little more than Mediterranean requirements.

⁴⁰ S.E. Morrison, History of United States Naval Operations in World War II: The Atlantic Battle Won (Boston, Little and Brown and Co., 1962), Vol. 1, pp. 203-204.

⁴¹ Karl Donitz, Memoirs: Ten Years and Twenty Days (Annapolis, Naval Institute Press, 1990), p. 344.

⁴² This calculation comes not from the modern desire to "quantify everything" but as a way to determine if the German effort was an efficient way to dispense resources even if the campaign was eventually lost i.e. was it a successful "cost-imposing" strategy.

⁴³ Loss of 33% of the merchant fleet is assumed based on both the German estimate and an average of the Allied estimate of the amount of time the average merchant ship lost waiting to form up in convoy or because convoy's had to proceed at reduced speeds to accommodate the slowest ships.

⁴⁵ U.S. Strategic Bombing Survey, German Submarine Industry Report (Washington, D.C., U.S. Government Printing Office, 1947), p.15.

⁴⁶ F. Lane, Ships for Victory: A History of Shipbuilding Under U.S. Maritime Commission in World War II (Baltimore, John Hopkins Press, 1951), p. 6.

⁴⁷ B.R. Mitchell, European Historical Statistics (New York, Facts on File, Inc., 1980), pp. 819-826. Note that in 1937, the Depression had greater effect on the American economy than the German one (which had commenced rearmament). However, I have not counted the fact Allied economic potential also had to oppose Italian and Japanese economic potential.

⁴⁸ Janet Manson, Diplomatic Ramifications of Unrestricted Submarine Warfare (New York, Greenwood Press, 1990), pp. 154-158.

⁴⁹ C. Blair, Silent Victory (Philadelphia, J.B. Lippencott and Co., 1975, p. xvi.

⁵⁰ U.S. Strategic Bombing Survey, The War Against Japanese Transportation (Washington, D.C., U.S. Government Printing Office, 1947), p. 47.

⁵¹ Joint Army-Navy Assessment Committee, Japanese Naval and Merchant Shipping Losses during World War II (Washington, D.C., U.S. Government Printing Office, 1947), p. vii.

⁵² Theodore Roscoe, U.S. Submarine Operations in World War II (Annapolis, U.S. Naval Institute Press, 1949), p. 493.

⁵⁴ Mark Parillo, The Japanese Merchant Marine in World War II (Annapolis, U.S. Naval Institute Press, 1993), p. 75.

⁵⁵ Strategic Bombing Survey, Japanese Transportation, pp. 60, 108-109. This study indicates there was a number of factors that were important, but that in most industries, industrial output was directly linked to imports of primary materials.

⁶³ Mark Parillo, "The Imperial Japanese Navy in World War II," in Reevaluating Major Naval Combatants of World War II (New York, Greenwood Press, 1990), p. 64.

⁶⁴ W.J. Holmes, Undersea Victory: The Influence of Submarine Operations on the War in the Pacific (Garden City, N.Y., Doubleday, 1966), p. 425.

⁷⁵ U.S. Strategic Bombing Survey, Japanese Naval Construction (Washington, D.C., U.S. Government Printing Office, 1946, p. 4.

⁷⁹ Strategic Bombing Survey, Japanese Transportation, pp. 4, 21. Iron Ore imports fell from 6.3 million tons in 1941 to 2.2 million in 1944 and 341,000 in 1945. As a result, steel deliveries to naval shipyards in 1944 were 58% of that delivered in 1941.

⁸¹ The Japanese calculated merchant marine efficency by a factor called Kakoritsu. Kakoritsu is computed by dividing actual cargo carried (in metric) tons in a given time period by the cargo carrying capacity of ship's in use during that period in that particular service.

⁸³ The delays were caused by the need to await sufficient merchants and escorts to form convoys and by the Japanese tactic of running some convoys near the coast- which lengthened the distances that needed to be traveled.

⁹² Ibid., pp. 213-215. Only 3% of deaths on New Guinea were due to combat. Some Japanese opted for suicide rather than the slow starvation that caused so many deaths.

⁹⁴ Thanks to the U.S. Strategic Bombing Survey, we have exact costs for Japanese ships (although the problems of inflation, particularly of Japanese currency, and exchange rates exist).

⁹⁵ 10% loss of time is based on the previously tabulated Kakoritsu i.e. loss of efficiency of 8% in 1942 and 1943 with substantially greater efficiency reductions later.

⁹⁶ B.R. Mitchell, International Historical Statistics, Africa and Asia. (New York, New York University Press, 1982), p. 761. U.S. Data from:

⁹⁷ Frederick Lane, Ships for Victory: A History of Shipbuilding Under the U.S. Maritime Commission in World War II (Baltimore, John Hopkins Press, 1951), p. 819. Based on cost of C2-S-B1 merchant built very efficiently by the U.S. Using this ship as a basis, I have underestimated real costs of ships lost.

⁹⁸ I have assumed that only vessels sailing for England carried cargo and that half of all losses were in ships sailing East across the Atlantic rather than West.

¹⁰¹ As previously discussed, Lane indicates U.S. shipbuilding costs were the lowest of our Allies.

¹⁰³ As previously noted, this number is about the average of Allied estimates and matches German estimates for time lost to convoying. The price of a ship is again based on the efficient cost of building liberty ships.

¹⁰⁴ Department of the Navy, Administrative History of the U.S. Atlantic Fleet in World War II (Washington, D.C., Government Printing Office, 1946), Vol. VI, pp. xv-xxxii.

¹⁰⁵ Friedman, op. cite., pp. 137-154. 1005 DDEs were ordered, 520 were constructed (of which 393 actually participated in the campaign). The order for 485 DDEs was cancelled, some of which were virtually finished. I have not included partial costs for the 485 DDEs.

¹⁰⁶ Kenneth Poolman, Escort Carriers in Trade Protection (London, Ian Allan, 1972), pp. 255-256.

Bureau of Ships, Ships Data- U.S. Naval Vessels (Washington, D.C., U.S. Government Printing Office, 1945), Vol. 1, p. 88.

¹⁰⁷ Friedman, op. cit., p. 140. The Hunts were light destroyers i.e. DDE's and were representative of DDE capabilities and costs.

¹¹⁰ ASW was a primary mission of fleet destroyers but not the only mission. Assuming that only half the cost of each fleet destroyer is attributed to ASW is a reasonable method to avoid assessing all of the cost of the DD against the primary threat.

¹¹¹ Navy Department, Administrative History of the U.S. Atlantic Fleet in World War II: Air Force Atlantic (Washington, D.C., 1946), Vol. VII Part 1, pp. 89-108.

¹¹² Irving Holley, Buying Aircraft for the Army Air Forces (Washington, D.C., Chief of Military History, 1964), Vol. 8 part 7, p. 560.

¹¹³ Submarines caused about two-thirds of all merchant losses. Assuming that aircraft were engaged in defending against the primary threat 50% of the time is reasonable and probably an underestimation of the actual ASW effort.

¹¹⁴ Roskill, op. cit., Vol II, pp. 363, 450-451, Vol. IIIa, p. 363, Vol. IIIb, p. 451.

¹¹⁵ Erich Groner, German Warships 1815-1945, (Annapolis, Naval Institute Press, 1990), Vol. II., pp. 40, 44, 68, 77, 85.

¹¹⁶ War Production Board, World Munitions Production, (Washington, D.C., War Production Board, Bureau of Planning and Statistics, 1944), p. 44. Much thanks to historians Timothy Francis (Naval Historical Center) and George Papadopoulos for this information.

¹¹⁸ Henry Davis, "Building U.S. Submarines in World War II", Proceedings, (July 1946), pp. 939.

U.S. Strategic Bombing Survey, German Submarine Industry Report (Washington, D.C., U.S. Government Printing Office, 1947), pp. 15-17.

¹¹⁹ As with the Allies, it is assumed that ships are only loaded half the time. Unlike the Allies, this is probably a substantial underestimation, because ships rarely traveled empty- raw materials were brought into Japan, and finished products and war materiel was sent out.

¹²⁰ As indicated in the text, this is an underestimation of the actual drop in Kakoritsu during the war.

¹²¹ David C. Evans and Mark R. Peattie, Kaigun: Strategy Tactics and Technology in the Imperial Japanese Navy, 1887-1941, (Annapolis, Naval Institute Press, 1997), pp. 364-9. U.S. destroyers were routinely produced in 5 months in more experienced yards, 6 months in less experienced yards. Japanese shipyards took about 12 months to produce a destroyer. Evans and Peattie discuss why U.S. shipyards were more efficient than the Japanese including much larger classes of ships, shipyard specialization, overall yard efficiency, simplified designs, all welded hulls.

¹²² World Munitions Production, op. cit., p. 51. A Japanese worker only produced 18% of what a U.S. worker on a per hour basis. The Japanese worked longer hours thereby reducing the difference in efficiency.

¹²³ Navy Department, Bureau of Supplies and Accounts, Naval Expenditures 1940, (Washington, D.C., Government Printing Office, 1941), pp. 217-8. This source provided what are probably the assessed value of the very old R, S classes.

¹²⁴ Bureau of Ships, op. cite., p. 282. U.S. Submarine costs are listed as approximately $3 million.

This cost does not include the purchase price of the 4 diesel engines, which I estimate at $300K.

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