Submarines (SS)

Photograph of a nest of submarines

The submarines of the Second World War were among the most sophisticated combat systems the world had yet seen. Designed to keep men alive in a hostile environment, filled with high-tech gadgets, and usually manned by a volunteer elite, they had an impact far beyond the investment made in them. Submariners strangled the economy of Japan and nearly strangled Britain.

Whereas the submarines of 1918 could dive to perhaps 250 feet and required half the crew to stand by the many valves, vents, and rudders used to submerge or surface, the submarines of 1939 could dive to better than 350 feet and had hydraulic controls that could be operated by a single man in the central control room. Fire control had also improved with the introduction of analog computers of various degrees of sophistication. By the end of the war, the latest American submarines could dive below 600 feet in an emergency.

Yet the submarines of this period were not true underwater craft. They were essentially surface torpedo boats with a limited capacity to operate underwater for purposes of stealth. In fact, a large percentage of kills were by submarines operating on the surface at night. This was particularly true of U-boats in the Atlantic, but it was also true of American submarines in the Pacific.

American Submarine Operations

Prior to war, American submarine doctrine was dictated by international prize rules that prohibited unrestricted submarine warfare. Any warship was fair game for a surprise attack, but merchantmen were supposed to be overhauled on the surface and their passengers and papers put “in a place of safety” before the ship could be sunk. Germany ignored these rules in the Atlantic, and when Japan violated the Hague Convention by the surprise attack on Pearl Harbor and the subsequent unrestricted sinkings of U.S. merchantmen in Hawaiian waters, the United States Navy decided to ignore the rules as well. U.S. submarines were plagued by defective torpedoes during the first two years of war, but after the faults were remedied, the submarines sank over half the ships of the Japanese merchant marine. Losses from other causes were sufficient to practically eliminate Japanese merchant shipping by the end of the war. American submarines also enjoyed significant successes against warships, accounting for six fleet carriers, three escort carriers, a battleship, twelve cruisers, over 40 destroyers, and numerous lesser warships and auxiliaries.

In addition to the antishipping role, American submarines sometimes supported guerrilla operations, particularly in the Philippines, or transported small raiding forces, as at Makin. During the air strikes preceding the Gilberts invasions, the Pacific Fleet experimented with deploying submarines near target atolls to rescue downed aviators. This proved so successful (a number of aviators being rescued and the morale of the aviator corps being greatly boosted) that the deployment of lifeguard submarines became a standard feature of carrier strike planning for the remainder of the war.

Japanese antisubmarine defenses never approached the sophistication of Allied defenses in the Atlantic. The Japanese Navy did not even establish an antisubmarine warfare school until March 1944. Convoying was adopted rather late in the war and too few ships and planes were assigned to escort duty. Small carriers that would have been ideal for escort were used as aircraft ferries instead. Japanese depth charges were too small and were usually set too shallow, at least until one of the stupidest men to ever darken the doors of Congress blurted out in a press conference why American submarines were able to evade counterattack. The Japanese did make effective use of minefields and developed a working airborne magnetic anomaly detector (Jikitanchiki), but the former were partially negated by new Allied mine detecting sonar, and the latter was limited in detection range and never available in adequate numbers. The Jikitanchiki was not very sensitive, requiring the plane to fly no more than 40 feet above the surface.

Japanese Submarine Operations

Most Japanese submarines fell into one of three families. The Junsen or cruiser submarines were developed for individual long-range patrol and reconnaissance, while the Kadai or fleet submarines were to operate in flotillas in conjuction with the surface fleet. The Ro were smaller coastal defense boats. Japanese submarines were generally somewhat larger than their Allied counterparts, but so much of their internal space was given over to equipment that their habitability was very poor, and Japanese submarine crews tired quickly on long patrols. Their large conning towers were excellent radar targets and their large size and lack of maneuverability reduced their ability to evade depth charge attack. Their crews had excellent night binoculars, giving them the same early advantage over the Allies in night actions as their surface forces, but this advantage eroded as the Japanse fell behind on radar development. The Japanese had a definite advantage in their excellent submarine torpedo, the Type 95, which was vastly superior to the miserable American Mark 14.

Although there is no evidence that the Japanese had any qualms about attacking merchantmen, Japanese submarine doctrine strongly emphasized attacks on warships. This was in keeping with the Japanese focus on the decisive battle that was supposed to be fought between the main Japanese and American battle lines somewhere in the Western Pacific. In order to compensate for the anticipated numerical superiority of the American fleet, the Japanese planned to wear down the Americans with attacks by submarines, light surface forces, and aircraft as the American Fleet crossed the Central Pacific. As a result, Japanese submarines never concentrated against the long and vulnerable Allied supply lines.

This was unfortunate for the Japanese. Although their submarines had some notable successes during the war, particularly the sinking of the Wasp during the Guadalcanal campaign, the employment of Japanese submarine forces was characterized by inflexibility and indecisiveness. A particular weakness was the use of ever-shifting picket lines, which persisted long after these had proven vulnerable to Allied hunter-killer groups, which were often guided to their victims by Ultra intelligence. Some of the poor management of Japanese submarine forces may have arisen from the fact that the submarine staff officers, even at the highest levels, were no higher in rank than commander, and so had little clout.

Those Japanese submarine squadrons that were deployed against merchant shipping, usually along the Australian coast or in the Indian Ocean, did well enough to show what might have been accomplished by the Japanese submarine fleet. However, Allied antisubmarine weapons and tactics were sophisticated almost from the start of the war, and Japanese submarines suffered heavily. It did not help that Japanese submarines tended to be rather slow-diving, both because they tended to be large and because they had excessively complicated linkages in their propulsion systems.

In contrast to the Allied advantages of superior intelligence and better antisubmarine defenses, the Japanese had much better torpedoes. Although some Japanese submarine commanders claimed that American merchantmen sometimes escaped destruction in shallow coastal waters, due to a tendency for Japanese torpedoes to run as much as 100 feet (30 meters) too deep before leveling off at the correct depth, the reliability, range, and explosive power of Japanese torpedoes were much superior to those of American torpedoes throughout the war.

Another misuse of Japanese submarines was their employment in transport operations to isolated garrisons. A special kind of container, called unkato, was developed that could be towed by a submarine and released to (hopefully) float ashore. The unkato was 135 feet (41 meters) long and could carry about 300 tons of cargo. Few actually reached their destinations, and a number of submarines were lost on such missions.

Antisubmarine Tactics

Because submarines were outgunned by almost all surface warships, the usual response of a submarine to a threat was to attempt to submerge and evade. Antisubmarine warships thus needed the capability of locating a submerged submarine, and suitable weapons for destroying it, once located. Submarines could be located using various forms of sonar and destroyed using either depth charges or antisubmarine mortars, such as Hedgehog. Depth charges were dropped or thrown on the estimated position of the submarine after being set to explode at its estimated depth, and relied on the powerful shock wave generated by their large explosive charge to buckle the hull of a nearby submarine. Antisubmarine mortars fired smaller charges fitted with contact fuses that had to actually hit the submarine to destroy it. The Americans also developed an acoustic homing torpedo for use against submarines, the Mark 24 or "Fido", but this seems to have been used only in the Atlantic.

Detecting the presence a submarine usually required spotting its torpedo tracks or the wake of its periscope. Detecting a submarine with hydrophones was quite difficult, and detecting it with sonar was all but impossible. Sonar was highly directional. This allowed sonar to get a good bearing on its target, but it also limited the usefulness of sonar for search, since it took several seconds to listen for a return on a single bearing. The sonars of the Pacific War were thus fire control systems rather than search systems, with effective search sonars not becoming available until 1946. Range was also limited, rarely exceeding 3000 yards (2700m) even under the most favorable conditions. Sonar was generally ineffective at speeds over about 10 knots, requiring "sprint and drift" tactics in which the antisubmarine warship had to periodically slow almost to a stop to make best use of its sonar. Early sonars could not determine depth with any accuracy and were unable to track a target immediately underneath the sonar. Thus, a submarine could sometimes evade a depth charge attack by maneuvering sharply just as the attacker passed overhead and lost sonar contact. The depth charge explosions themselves blinded sonar, and a submarine that survived a depth charge attack could sometimes break contact behind the "wall" of sonar interference created by the depth charges.

The British developed the "creeping attack" to overcome these deficiencies. One antisubmarine ship would maintain sonar contact with the sub while guiding a second antisubmarine ship that closed in at low speed with its own active sonar turned off. This form of attack was extremely difficult for the submarine to evade. Another effective technique was to "crowd" the submarine with three escorts saturating the target area with depth charges.

Aircraft proved highly effective for antisubmarine work. Because submarines had only a very limited speed and endurance when submerged, they cruised on the surface and were vulnerably if surprised by a patrolling aircraft. Even if they crash dived in time to avoid air attack, their effectiveness was greatly reduced because they could not search for distant merchant ships or maneuver to attack them while submerged. The ideal antisubmarine aircraft had a long range for extended patrols; had adequate sensors for detecting submarines; could loiter at low speed over a suspected contact; and could carry a large number of depth charges. Both sides in the Pacific used flying boats and long-range bombers in the antisubmarine role, but the Japanese also built a dedicated antisubmarine aircraft design (the Q1W "Lorna") and experimented with antisubmarine autogyros. The latter had inadequate range and carrying capacity, but prefigured the more effective antisubmarine helicopters of the postwar world.