War in the Pacific: The First Year
A Guide to
the War in
the Pacific

Allied Pacific Counteroffensives

South & Central Pacific

China-Burma-India, Aleutians

Marines & Rikusentai

Submarines in the Pacific


War in the Pacific: The Pacific Offensive

The Silent Service: Submarines in the Pacific

U.S. submarine commander looking through periscope
A U.S. submarine commander observes enemy ships through a periscope. American subs inflicted significant losses to Japanese shipping during the Second World War.

Among the U.S. Navy's deadliest and arguably its most effective weapons were its submarines. The unrestricted submarine warfare during the Second World War in the Pacific knew no bounds, no limits concerning the sinking of Japanese ships. Shrouded in secrecy, the "Silent Service" depended on stealth for its success and resourcefulness to counter Japanese countermeasures. The United States, early on, recognized the importance of the Pacific sea routes to the Japanese. A strong merchant marine was essential to Japan's wartime economy. Its ships imported vital oil, iron ore, bauxite, rubber, and foodstuffs; Japan sent by ships armaments and ammunition, aircraft, and soldiers to support the forces committed to defeating the ABDA powers and, later, following the Midway and Guadalcanal battles, with the intent of making the Allied counteroffensive so costly in lives that the soft Americans would opt for peace. The Pacific Ocean was the lifeline to Japan's imperial success; sinking ships would cripple the commerce of the Rising Sun.

Postwar records compiled by the Joint Army-Navy Assessment Committee indicate Japan lost 686 warships of 500 gross tons (GRT) or larger, 2,346 merchantmen, and a total of 10.5 million GRT to submarines during 1,600 war patrols. Only 1.6 percent of the total U.S. naval manpower was responsible for America's success on its Pacific high seas; more than half of the tonnage sunk was credited to U.S. submarines. The tremendous accomplishments of American submarines were achieved at the expense of 52 subs with 374 officers and 3,131 enlisted volunteers lost during combat against Japan; Japan lost 128 submarines during the Second World War in Pacific waters. American casualty counts represent 16 percent of the U.S. operational submarine officer corps and 13 percent of its enlisted force.

During the early years of the Pacific war, submarine warfare was an inexact and faulty operation. Prior to America' sentry into World War II, the United States was a signatory to numerous international treaties decrying unrestricted submarine warfare against merchant shipping. Allied merchant shipping in the Atlantic Ocean took a merciless beating from German U-boats, despite President Franklin D. Roosevelt's policies that by June 1940 were aimed at providing Britain and her allies the tools of war. By the autumn of 1941, following the stationing of U.S. Marines in Iceland, lives were lost as U.S. destroyers were attacked by German U-boats.

U.S. submarine
A typical American submarine, the U.S.S. Salmon (SS 182), survived one of the most severe enemy depth charge attacks of WWII.

America's policy on submarine warfare changed following the Pearl Harbor attack on December 7, 1941. Other problems had to be overcome, as well, including the belief that aircraft, sonar, and depth charges would make the submarine vulnerable to enemy naval and air attack. Peacetime submarine commanders' strategies, in retrospect, were also archaic: attack from deep submergence with sonar. Considered overly hazardous were day and night periscope attacks, as well as night surface attacks; operating within 500 miles of an enemy air base was considered suicidal. The devastating attacks by U-boat wolfpacks had demonstrated the fallacy of these concerns.

A final, but major, obstacle that struck at the U.S. submarine forces' Achilles Heel early in the war was defective torpedoes. Developed during peacetime, but never fully tested against targets, torpedoes were considered the most lethal weapon of the U.S. naval arsenal. Swift and silent, these underwater missiles could sink or disable wartime and merchant shipping. The torpedo had two exploders, one that detonated on contact with an enemy ship, and a secret "magnetic exploder" that would detonate beneath the keel of a ship without contact. But, as America's submarine force steadily increased the usage of torpedoes during the early phases of the war, it was discovered that the torpedoes would run much deeper than designed, thus making the magnetic exploder inoperative. It was further discovered that the magnetic exploder was often defective, exploding well before reaching the target. Corrections were made 21 months after America's entry into the war, and, despite orders to the contrary by officers of the Torpedo Bureau, submarine captains discontinued use of magnetic exploders.

Japanese ship sinking
A Japanese ship sinks to the bottom in this photograph taken through the periscope of an American submarine.

Despite the initial faults of America's submarine force, there was optimism. For example, between 1941 and 1945, U.S. Navy codebreakers deciphered Japanese sailing dates, courses, speeds, and routes of naval convoys and formations, unbeknownst to the Japanese. This information was supplied to the U.S. submarine force, which would lie silently in wait for unsuspecting ships. By 1943, 22 Japanese warships and 296 merchant ships would be sent to the bottom, due to workable torpedoes and changed underwater tactics.

Increased submarine proficiency, founded on an all-volunteer service (submariners made fifty percent extra pay), new long-range fleet type models, and the successes of the U.S. Navy codebreakers, by August 1944, found the "Silent Service" inflicting prohibitive losses on the Emperor's merchant marine, scoring key successes against Japanese warships that insured victory in the Battle of the Philippine Sea, and a blockade of the home islands that was strangling the Japanese economy.

Acquiring this newly found naval status had been an arduous and difficult affair. Surviving vessels of America's Asiatic Fleet were redeployed and moved from Manila Bay to first Darwin and then Freemantle, Australia, in early 1942 and a new commander, Admiral Charles Lockwood, placed in charge. Lockwood's energy and enthusiasm revamped submarine tactics, to be employed by the newer subclasses. This was dictated because Japanese submarines had scored successes. On September 15, 1942, the Japanese submarine I-19, firing a spread of four torpedoes, sank the aircraft carrier Wasp and seriously damaged North Carolina, one of Uncle Sam's newest and most powerful battleships. The previous month, the aircraft carrier Saratoga had been torpedoed and put out of action for months. These losses, along with that of Wasp's sister Hornet, to air attack on October 27, seriously crippled U.S. naval airpower in the weeks that the battle for Guadalcanal hung in the balance. The situation for Lockwood and America's submariners was slowly improving by late 1942: U.S. subs in 1942 sank 180 Japanese ships for a total of 725,000 GRT; yet Hitler's U-boats sank 1,160 Allied ships of more than 6 million GRT.

During 1943, Lockwood assumed control of ComSubPac (Command of Submarines, Pacific) in Pearl Harbor. The Central Pacific campaign was mapped out by command headquarters for the assaults on Tarawa and Makin, and submarines played a pivotal role. The German strategy of "wolfpacking" was adopted. It called for coordinating submarine attack groups during 1943. More submarines, of larger size and firepower, were being built in American shipyards. New torpedo designs added the necessary punch for U.S. subs to eventually penetrate the once forbidden Sea of Japan. By year's end, American sub improvements had netted a total of 1.5 million GRT sunk. Eighty-six American subs had also rescued 380 downed aviators from Pacific waters.

American submarines flexed their naval might following the recapture of Guam in July-August 1944. U.S. subs based on Guam and Saipan imposed a virtual blockade against Japan. Few ships entered or left Japanese waters without being attacked or sunk by submarines. Japan ran out of oil for her naval armada, gasoline for aircraft and tanks, steel and aluminum for industry, and food for her people. By August 1944, the sea war was no longer in doubt-three of Japan's remaining five fleet carriers had been sunk, and Japan's navy ceased thereafter to be a factor in the outcome of the war.

naval vessels
U.S. submarines return to port after a successful patrol, as a PBY aircraft scouts for enemy ships at upper left.