also seen as a level bomber. The big internal bay could accommodate four 500lb, two 1000lb or one 2000lb bomb. In July 1942 VT-6 experimented with glide bombing. Aircraft dove at a 45 to 60° angle from 6500ft, releasing their bombs at 2500ft. They found that they could place their bombs within 40ft of a moving target. The squadron commander recommended removing all horizontal bombing gear, but BuOrd kept the Norden bombsight because it felt that under some circumstances the earlier technique might still be useful (it turned out that pilots used only the stabilised bombing approach part of the Norden, as an autopilot for use during long flights; in 1944 it was replaced in new production aircraft with an autopilot). Glide bombing did not require the displacement gear (crutch) used by dive bombers to keep their bombs away from their propellers as they dove; at a 60° angle the Avenger would not be struck by its own bomb. However, it had never been stressed for glide/dive bombing, and occasionally Avengers disintegrated during bombing dives. The aircraft could not afford the required 400–600lbs of strengthening, so Grumman added strength at what it estimated were critical points. Accelerometers were installed to indicate to pilots that they were approaching dangerous conditions. The problem was not really solved until March 1945, when Eastern Aircraft (which was producing Avengers under license), redesigned the Avenger using higher-strength alloy and at the same time redesigned the wing hinges. This TBM-4 was scheduled to enter production in August 1945, when the war ended the Avenger programme. These Avengers are shown on 15 March 1950.
There was little chance that a single torpedo bomber could hit a manoeuvring ship. Those on the target ship would see the bombers drop their weapons, and the ship was nearly as fast as the torpedoes. Evasion often succeeded. During the inter-war period, tacticians developed an answer. Aircraft would attack in groups (equivalent to firing a spread of torpedoes from one direction). At least two groups would attack together, from both bows.18 At least in theory this ‘hammerhead’ or ‘hammer and anvil’ approach would ensure that however the target ship manoeuvred, some torpedoes would hit. The faster the target, the more important to ensure that she had little or no manoeuvring time after torpedoes were in the water. That favoured minimum-range attacks at low level. Much depended on the element of surprise. The faster the attacker, the less chance the target had to evade.19 It also helped to put the torpedo into the water as close as possible to the target – but that made the attack more dangerous.
A November 1942 British description of German convoy attack tactics was that aircraft typically approached at about 150ft from astern or on the quarter of a convoy, although occasionally they circled outside gun range to gain better positions. Sometimes they turned towards the convoy individually and then turned away, to draw gunfire. Final approach and release were generally from bows or quarter at 50–80ft, with an outside limit of 180ft. Average dropping range was 1500 yds, with outside limits of 500 and 4000 yds. Attacks on convoys were generally by five or six aircraft, with a maximum of ten. Unescorted ships were generally attacked singly, though at times two or three made concerted attacks. After attacking, aircraft turned away and made off at low altitude. Typically torpedo attacks were made in conjunction with dive- and high-level bombing attacks. At times the Germans (e.g. against Russian convoys) dropped from unusually great heights. In one such attack, against Convoy PQ17 in 1942, torpedoes were seen to bounce more than their own height out of the water.
A Mk 13 torpedo about to be loaded on board a TBM-3 Avenger displays two of the three modifications which made the torpedo effective at high drop speeds and altitudes: the wooden ‘pickle barrel’ around the nose and the box tail. The third new feature, the tail ring, is hidden by the box tail. Unlike the British and the Italians, the US Navy did not adopt long-span air tails because it carried its torpedoes internally (even the Devastator carried its weapon semi-internally). This torpedo was being loaded on board the light carrier San Jacinto during the battle of Leyte Gulf, October 1944. US torpedo tactics changed radically during the war. In 1941 standard practice was to approach a low altitude. During the autumn of 1941 VT-3 developed a new tactic, in which the aircraft approached the target at high altitude, then dove to attack altitude near the target. That improved the pilots’ view of the target, and the high-speed dive to drop altitude improved protection against enemy anti-aircraft fire.
The B5N (‘Kate’) was the standard Japanese carrier torpedo bomber in 1941, the aircraft which attacked Pearl Harbor and which fought at the Coral Sea and at Midway. At the time it was the highest-performing carrier torpedo bomber in the world (though one might say that the others, the Swordfish and Albacore and the US Devastator, were not very impressive). Design work (7-Shi specification, i.e., FY 33) began in 1932, about two years earlier than that on the Devastator. After none of the designs offered proved satisfactory, the navy issued another specification (10-Shi: 1935) calling for a maximum speed of 180kts and a range of 540nm carrying the usual 800kg torpedo. It first flew in January 1937. The version in service at the outbreak of war in 1941 was B5N2, which offered higher performance to deal with modern fighters: maximum speed was 204kts, and normal range was 528nm. (Philip Jarrett)
The B6N Tenzan (‘Jill’) was the planned replacement for the ‘Kate’ which carried out Japanese carrier torpedo attacks at the outset of the Pacific War. It was designed to a 1939 (14-Shi: FY40) specification calling for a maximum speed of 250kts (200kts cruising speed) and a range of 1000nm with the standard 800kg load (torpedo or bombs). The speed was comparable with that of the US Avenger designed at about the same time, and the range was chosen to support the preferred tactic of attacking beyond the enemy’s attack range. The Tenzan was designed at a time of steeply rising engine performance, its engine being about 80 per cent more powerful than that of its predecessor. Although the prototypes were complete in the spring of 1941, the Tenzan had serious teething troubles, and it did not enter production until 1943. It fared poorly against US naval fighters in its first major engagement, the battle of the Philippine Sea in June 1944. (Philip Jarrett)
In the Mediterranean the British found that barrage fire could force Italian torpedo bombers to release their weapons at greater ranges, so that after 1940 they were relatively ineffective against fleet units (but not convoys).20 In addition to conventional torpedoes, the Italians had air-launched circling torpedoes specifically for use against convoys, roughly as the Germans used pattern-running torpedoes launched by submarines. Circular runs were more efficient than the German zigzag inside a convoy, and the aircraft did not have to fear a torpedo coming back at it.21 The Germans later adopted the larger of the two Italian circlers.
Because a torpedo bomber approached almost horizontally, it was susceptible to the same sort of smokescreen which would frustrate an attacking ship. Most wartime radars were not good enough to permit blind attacks. Several navies found smokescreens effective against torpedo bombing.22
Torpedo bombing was the dominant form of wartime night anti-ship attack because of its relative simplicity and because a ship presented so large a target. In 1943–4 the Imperial Japanese Navy used land-based long-range G4M (‘Betty’) torpedo bombers at night (the US Navy did not yet have many carrier-based night fighters). For example, one torpedoed the US carrier Intrepid in her rudder in November 1943. Initial attacks were conducted by single aircraft. The target ship might be unaware of the attack until the torpedo struck, hence would not take evasive action. In order to line up its target visually, the bomber generally laid a path of floating flares the movement of which indicated windage. It then turned back and flew down the path to drop its torpedo. This type of attack made the development of blind-firing anti-aircraft weapons more urgent.
Aichi’s B7A Ryusei torpedo bomber (‘Grace’) was part of the 16-Shi (1942) programme. It was intended to extend the reach of Japanese carriers
