Allied submarines in the Pacific War

• 1. Introduction

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  Allied submarines in the Pacific War quietly dismantled the Japanese empire from beneath the ocean surface, yet their campaign remains one of the least-publicized feats in military history. A total of 283 Allied submarines were active across the Pacific and Southeast Asia between 1941 and 1945. By the time the guns fell silent in August 1945, the Japanese merchant fleet had been reduced to less than a quarter of its prewar tonnage. What made that destruction possible, and what made it so difficult to talk about? The answers involve faulty weapons, deliberate silence, aggressive admirals, and a shift in naval doctrine that broke more than a century of international law.

• 2. A Fleet Built for the Wrong War

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  On the 7th of December 1941, the U.S. Navy had 55 fleet submarines and 18 medium-sized S-boats in the Pacific, with another 38 elsewhere and 73 under construction. Pre-war doctrine for all major navies held that submarines existed to support the surface fleet. Attacking merchant ships was a secondary role, one hedged by the prize rules of the London Naval Treaty, which the U.S. had signed.

  U.S. submarines were formidable machines on paper. They carried long range, a fast cruising speed, and a heavy armament of torpedoes. Amenities like air conditioning and fresh water distillation units made them better suited for tropical patrols than German U-boats. Their commanders and crews were regarded as an elite, with a strong esprit de corps.

  But the boats also carried a hidden catastrophe. The Mark 14 and Mark 15 torpedoes had been mass-produced without adequate testing. Four major engineering faults left them with only a 20% success rate from December 1941 through late 1943. During the 1941-42 Philippines campaign, the Asiatic Fleet's 23 modern submarines failed to sink a single Japanese warship, even when scoring direct hits, because the torpedoes refused to explode.

  The Netherlands also maintained a submarine force based at Surabaya to protect the Netherlands East Indies. Britain had stationed 15 modern submarines in the Far East as of September 1939, organized into the 4th Flotilla at the China Station. Both British flotillas were withdrawn by mid-1940 to reinforce the Mediterranean Fleet, leaving no British boats available in the Pacific in December 1941.

• 3. Unrestricted Warfare

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  Six hours after the Japanese attack on Pearl Harbor, the U.S. Navy Chief of Staff ordered Pacific commanders to "execute unrestricted air and submarine warfare against Japan." The order authorized attacks on any warship, commercial vessel, or civilian passenger ship flying the Japanese flag, without warning. Thomas C. Hart, commander in chief of the U.S. Asiatic Fleet, issued the same order independently at 03:45 Manila time, knowing that Chief of Naval Operations Harold "Betty" Stark intended to issue it.

  This directive broke sharply with the London Naval Treaty, with long-standing U.S. policy defending freedom of the seas, and with the pre-war doctrine of a decisive battleship engagement. It appears to have been executed without the prior knowledge or consent of the civilian government.

  The Pacific Fleet's submarines had emerged unscathed from Pearl Harbor and left on their first offensive war patrol on the 11th of December. The Asiatic Fleet's 27 submarines went into action that same day, patrolling the waters around the Philippines and Indochina. Inadequate prewar planning had made no provision for defensive minelaying or for positioning submarines off enemy harbors. The Asiatic Fleet's bid to counter the Japanese invasion of the Philippines failed, and its surviving submarines withdrew to Surabaya.

  In December 1941, five Dutch submarines attacked the Japanese invasion fleet off Malaya, sinking two merchant ships and damaging four others. Three of the attackers were sunk. The Asiatic Fleet's submarine force eventually evacuated to Fremantle, Western Australia, on the 1st of March, having sunk 12 Japanese ships at the cost of four U.S. boats.

• 4. Japan's Dependence on the Sea

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  Japan's vulnerability had been calculated before the war. Japanese planners estimated the nation required 5,900,000 long tons of shipping to maintain both the domestic economy and the military during a major conflict. At the time of the Pearl Harbor attack, Japan's total shipping capacity stood at 7,600,000 long tons: 6,400,000 from the merchant fleet itself and another 1,200,000 from smaller craft.

  Despite knowing that sea transport was essential, the Japanese military seriously underestimated the threat Allied submarines would eventually pose. Early Allied submarine ineffectiveness reinforced Japanese overconfidence. Anti-submarine warfare was assigned low priority. Few warships or aircraft were allocated to convoy protection. Japanese destroyers formed the bulk of convoy escorts. They were capable night fighters but fell short of Allied equivalents in sonar and radar. Japanese naval doctrine on commerce defense was, by the source's own accounting, very bad.

  The Japanese merchant fleet's decline tracked the growing competence of U.S. submarines almost exactly. The fleet held 6,384,000 tons at the start of December 1941. By the end of 1942 it had dropped to roughly 5,942,600. By the end of 1943 it had fallen further to 4,494,400. The end of 1944 saw it at 2,564,000 tons. By the final months of the war in 1945, less than 1,500,000 tons remained afloat. Japan never successfully developed a cost-effective destroyer escort suited for convoy duty, and its industry lacked the capacity to replace what it was losing.

• 5. Fixing the Weapon

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  Admiral Charles A. Lockwood drove the effort to fix the Mark 14 torpedo, but the problems were not fully resolved until September 1943. Two full years of patrols were fought with weapons that failed on contact. Poor torpedoes are believed to have claimed at least two U.S. submarines.

  Lockwood also replaced cautious submarine skippers with more aggressive commanders. Signals intelligence broke the Japanese "maru code" in January 1943, after a prewar gaffe by U.S. Customs had caused Japan to change the cipher in the first place. American aircraft added to the pressure through aerial minelaying in Operation Starvation.

  The cumulative effect of these improvements hit Japan in 1943 and 1944 with devastating force. In 1944, U.S. submarines destroyed the Japanese fleet carriers Shokaku and another carrier in the Battle of the Philippine Sea. They sank or disabled three Takao-class cruisers at the opening of the Battle of Leyte Gulf. That same year they sank the battleship Musashi, the only Japanese battleship lost to a submarine. The fleet carriers Unryu and Shinano also went down; Shinano was the largest vessel ever sunk by a submarine. By January 1945, U.S. submarines had effectively destroyed the Japanese merchant fleet.

  In 1943, U.S. Congressman Andrew J. May publicly disclosed that Japanese depth charges were not being set deep enough to destroy American submarines. Whether May's disclosure directly prompted a Japanese tactical adjustment has never been definitively established, but Japanese anti-submarine warfare did grow more effective afterward, particularly following the introduction of radar into the Imperial Japanese Navy.

• 6. British and Dutch Boats

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  Britain's submarine force in the Far East expanded substantially from August 1943 onward. The British Eastern Fleet held responsibility for submarine operations in the Bay of Bengal, the Strait of Malacca as far as Singapore, and the western coast of Sumatra to the Equator. Larger Japanese cargo ships rarely operated in this region. British submarines chiefly hunted small craft in inshore waters, interdicting supplies bound for Burma and attacking U-boats operating from Penang.

  By October 1944, the Eastern Fleet's submarines had sunk a cruiser, three submarines, six small naval vessels, 40,000 long tons of merchant shipping, and nearly 100 small vessels. In late 1944, the 8th Flotilla transferred to Fremantle with 11 British and Dutch submarines, operating in the Java Sea under the U.S. 7th Fleet. The 4th Flotilla and the newly formed 2nd Flotilla remained at Ceylon.

  By March 1945, British boats had closed the Strait of Malacca entirely, cutting off any sea-borne supplies to Japanese forces in Burma. A British submarine torpedoed and sank a heavy cruiser in the Bangka Strait, taking down approximately 1,200 Japanese army troops. Three British submarines were sunk by the Japanese during the entire war.

  Britain also deployed a flotilla of midget submarines: the Fourteenth Flotilla, equipped with six XE-class submarines, arrived in Australia in April 1945 and nearly disbanded in May for lack of targets. On the 31st of July, XE4 cut the submerged Singapore-Saigon telegraph cable near Cape St. Jacques in French Indochina, while XE5 severed the Hong Kong-Saigon cable close to Lamma Island in Hong Kong. Simultaneously, XE1 and XE3 penetrated the Straits of Johor and severely damaged a Japanese heavy cruiser with limpet mines.

• 7. The Human Cost

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  Some 16,000 American submariners served during the Pacific War. Of those, 375 officers and 3,131 enlisted men were killed, a fatality rate of around 22%. That figure paled beside the roughly 70% fatality rate suffered by German U-boat crews, but it made the submarine service one of the most dangerous assignments in all of the American armed forces.

  Fifty-two U.S. submarines were lost in the war, all but one in the Pacific theater. Two were lost to friendly fire: Dorado (SS-248), possibly also a victim of a German mine, and one other. At least three, including Tulibee, Tang, and Grunion, were lost to their own defective torpedoes. Six more were lost to accident or grounding. Eight went missing on patrol and are presumed sunk by Japanese mines.

  Allied submarines also inflicted enormous suffering on the enemy, and sometimes on their own. Allied submarines sank an estimated 44 Japanese troopships with more than 1,000 casualties each, with 33 of those attacks producing such losses. But the same campaign also sank ships transporting Allied prisoners of war and rōmusha slave laborers. An estimated 10,800 Allied POWs died at sea as a result. The historian Donald L. Miller placed the total higher, asserting that approximately 21,000 Allied POWs died at sea, with roughly 19,000 killed by friendly fire.

  Seven submarine captains received the Medal of Honor for their service, including Samuel D. Dealey, John P. Cromwell, and Howard W. Gilmore, all of whom were killed in action.

• 8. Aftershocks and Reckoning

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  By the end of the war, U.S. Navy submarines had sunk around 1,300 Japanese merchant ships and roughly 200 warships. The war against Japanese shipping was later judged to be the single most decisive factor in the collapse of the Japanese economy.

  The campaign also resonated far beyond the Pacific. At the Nuremberg Trials, Großadmiral Karl Dönitz was accused of waging unrestricted submarine warfare in the Battle of the Atlantic. Allied actions in the Pacific were held to be a mitigating factor in reducing his sentence. Admiral Chester Nimitz provided Dönitz with a written statement asserting that U.S. boats had behaved no differently than German ones. The International Military Tribunal's official judgment cited that statement as part of its reasoning for declining to assess Dönitz's sentence on the basis of breaches of the international law of submarine warfare.

  The campaign's other legacy was the airmen it saved. From early 1944, U.S. submarines were assigned to rescue crews forced down over the ocean. By the end of the war they had pulled 504 airmen from the water, among them George H. W. Bush, who later became the 41st President of the United States.