The U.S. Navy believed it could weaken Japan’s grip on Asia’s resources without depending on strategic bombardment or guerrillas. It proposed the destruction of the Japanese merchant marine by unrestricted submarine warfare, since Japan’s war industry and the fabric of its society, like Britain’s, depended upon the uninterrupted flow of raw materials and food to the Home Islands. Although the navy had developed its own submarine force to support fleet operations, newer classes of American submarines (principally the Tambor and Gato classes, also known as fleet boats) had the range to reach the trade routes of the Western Pacific, even the waters of the Home Islands. Moreover, like the U.S. Navy, the Japanese Navy had paid little attention to anti-submarine warfare or the organization of convoys. Within a week of Pearl Harbor, three American submarines were on their way to Japanese waters; other boats stationed at Cavite, the Philippines, looked for targets. Yet for almost two years the submarine forces of the Pacific Fleet, divided between Australia and Hawaii, proved no more effective than bombers from China. The limitations of American commerce raiding early in the war provided one more reason why the Allies had no choice but to fight the Japanese Army and Navy somewhere in the Pacific.
The U.S. Navy’s submarine service had developed a prewar reputation for excellence that rivaled naval aviation or the German submarine force. The navy carefully selected crew members for their intelligence, technical skill, and emotional stability; faced with stressful living conditions and dangerous duty, submariners received extra pay and special comforts while ashore. Officers enjoyed the prospect of challenging assignments and command at ranks lower than their more comfortable peers on battleships and cruisers. The safety concerns and expenses of peacetime training, however, did not test submarine commanders, and in the war’s first year one-third of them lost their assignments because of ineffectiveness. Nevertheless, the human material of the force remained outstanding from first to last. It had to be, for the U.S. submarine force endured the highest risks of any American combatants in World War II. Almost 22 percent of its deployed crews were killed on wartime patrols (3,500 of 16,000 sailors), the highest percentage of deaths in any American combat arm.
The navy built quality submarines to match its superior submarine crews. Breaking away from the practice of building ships in government shipyards, navy submariners developed a close working relationship with German and American makers of diesel and electric engines and steel pressure hulls; the most influential of the companies were the Electric Boat Company (Groton, Connecticut), Maschinenfabrik-Augsburg-Nürnberg (Germany), Allis-Chalmers, General Electric, and General Motors. Submarine commanders worked closely and persuasively with their counterparts in the Bureau of Engineering, the navy’s department for submarine construction. The course of submarine development was not straight or smooth, but by 1941 the American submarine force believed correctly that it had boats with superior diesel engines for rapid surface movement (maximum 20 knots), superior electric engines of sufficient safety and durability for underwater attacks, and welded hulls and machinery that met the challenges of the unforgiving ocean and enemy. This assessment proved correct.
Given the navy’s expectations, the combat performance of submarines in 1942 and 1943 was just another example of blighted hopes. In 1942 the Japanese merchant marine lost only 180 ships (including two oil tankers) of 800,000 tons; the next year American submarines improved the score to 335 ships (23 tankers) of 1.5 million tons, still not crippling losses. The Japanese replaced the lost tonnage with relative ease in 1942; their annual loss represented only one-sixth of Allied losses to German submarines. Japanese merchant tonnage remained close to 5 million tons until mid-1943. Since Japanese anti-submarine warfare efforts cannot explain this pallid record—the U.S. Navy lost only 7 boats in 1942 and 17 in 1943—the disappointment had to be self-inflicted.
It was. As with every military force in World War II, American submariners had to make tactical adjustments, but their principal problem was defective torpedoes. American boats went to war bristling with torpedoes and launch tubes; they carried a normal load of 24 “fish” fired from six launching-tubes forward and four aft. The Bureau of Ordnance had outdone itself in developing the Mark XIV torpedo, almost 15 feet in length, capable of speeds up to 46 knots over a range of 4,500 yards. The Mark XIV carried 500 pounds of TNT, soon replaced by almost 700 pounds of Torpex, an even more devastating explosive—provided the warhead actually exploded.
Therein lay the problem, for the Mark XIV carried two types of detonators, magnetic field and contact, and neither worked correctly. Moreover, the Bureau of Ordnance’s engineers had calibrated the torpedoes’ depth settings 10–15 feet in error due to tests without a full explosive load. Through hard experience, submarine commanders determined that the complex firing pin for the magnetic exploder had a design flaw that made it explode prematurely or not at all; since the exploder was so highly classified, few knew what the problem might be until one courageous captain pulled a warhead apart and tested it. Convinced the magnetic exploders would not work, he and others disarmed them and went to the contact exploder. This detonator also failed to work every time, again because of a design problem in the firing pin that could, happily, be reengineered and compensated for by changing tactics. In the course of coping with the Mark XIV warhead problems, the submariners discovered the depth setting problem as well. Commander Tyrell Jacobs, who had discovered the exploder problem, actually conducted tests in combat, and another captain maneuvered under fire to launch four Mark XIVs at an anchored freighter. Launched with varied depth settings, none damaged the ship, and one exploded on the beach. The skipper then sank the freighter with two older models.
Outraged at the torpedo problem, Rear Admiral Charles A. Lockwood, Hawaiian force commander, conducted his own unauthorized tests and finally won admission from the Bureau of Ordnance that its engineers had erred. By the end of 1943—a year in which they had fired ten “fish” for every ship sunk—American submarines finally had dependable warheads. Combined with new search radars to detect enemy aircraft and surface vessels and active and passive sonar for underwater detection, the submarines enjoyed substantial technical advantages over the Japanese. They also received better guidance for intercepting targets, provided by the Ultra code breaking system, which had been denied U.S. submarines for much of 1942–43 for fear of capture and compromise. The Japanese merchant fleet did not have long to live.
The early performance of the Japanese submarine force was not much better, despite its elite sailors, its well-built, modern boats armed with a variant of the Model 95 Long Lance torpedo, and an adequate sonar and radar capability. The force was not large, but the Japanese Navy could draw on 56 I-Class boats comparable with the U.S. Navy’s fleet boats. Nevertheless, the Japanese submarine force mounted no real campaign against Allied shipping in the Pacific. Although the force increased to almost 200 boats before the war’s end, Japanese submarines sank only 171 warships, naval auxiliary vessels, and merchant ships of approximately one million tons. To be sure, Allied vessels carrying raw materials to North America traveled routes at the limits of Japanese range, but the Allied war effort required the massive shipping of troops, weapons, and supplies to the South Pacific and Australia well into 1944 and then north to the Philippines. Similar convoys followed the Pacific Fleet westward in late 1943. The Japanese did little to impede the flow of materiel. From December 1941 to July 1942 their submarines and aircraft sank 21 merchantmen, most along the Malay barrier and in the Indian Ocean. Over the next 18 months the Japanese sank only 10 merchantmen, 9 in the Southwest Pacific or Indian Ocean.
Allied losses soared with the introduction of the kamikaze suicide aircraft, which simply crashed into their victims; but the 14 ships sunk and 53 damaged in Philippine waters and northward owed nothing to the I-boats. With little to show for their sacrifice, the Japanese Navy lost 128 submarines in World War II (112 to the Americans), and the percentage of Japanese submariners lost exceeded even that of the U-boat force.
The Japanese submarine failure did not lie in technology but rather in faulty operational doctrine and poor communications security. The Japanese Navy expected its boats to attack enemy warships. Thus, Japanese submarine captains displayed much more aggressiveness in attacking U.S. warships than merchant ships. Yet, battleships and carriers had destroyers and destroyer-escorts to protect them. American anti-submarine operations improved with more escort vessels, aircraft, radar and sonar, and experience. In addition, served with Ultra information on Japanese submarine deployments, anti-submarine task forces consistently found Japanese submarines in predictable cordons in front of the Pacific Fleet. In one memorable twelve-day period in 1944, three U.S. destroyer-escorts sank six I-boats. Japanese submarines did not even specialize in operations against U.S. submarines until late in the war, when the Home Waters had become a pond for American boats. During the entire war, Japanese submarines sank only one American submarine, whereas U.S. submarines accounted for 17 Japanese submarines lost. The Japanese Navy’s commitment to heroic naval battles produced one of the larger missed opportunities of the war—the chance to destroy the troop transports, oilers, and ammunition ships on which the Allies depended in the South Pacific.
