Throughout the first year of the war in the Pacific during World War II the USAAF was relatively ineffective against ships. Indeed, warships in particular proved to be too elusive for conventional medium-level bombing. High-level attacks wasted bombs, and torpedo attacks required extensive training.
As told by Mark Lardas in his book B-25 Mitchell vs Japanese Destroyer, Battle of the Bismarck Sea 1943, Lt Gen George Kenney (the Fifth Air Force Commander in New Guinea) ended 1942 frustrated about the performance of his bombers against Japanese ships at sea. Medium level horizontal bombing had proven to be generally ineffective against moving vessels. Even large and slow transports had managed to evade most bombs dropped from altitudes above 5,000ft. Drop enough bombs on such a target and one or two might hit. Bombing agile and fast destroyers from those altitudes was hopeless.
His aircraft needed to go lower. That exposed them to light antiaircraft fire, which had to be countered. Furthermore, using standard attack profiles that saw bombers approaching broadside to a ship required exquisite timing to score a hit. Typically, only one bomb would hit when multiple bombs were dropped. Kenney assigned the task of improving the ability of his medium and strike bombers to suppress antiaircraft fire to Maj Paul Gunn of the 90th BS/3rd BG, who developed a strafer version of the A-20 and B-25.
Meanwhile, Maj William Benn, commanding the B-17F equipped 63rd BS/43rd BG, was also getting frustrated with his aircraft’s inability to hit enemy warships. He began experimenting with a technique called skip bombing. He would fly a B-17 “on the deck” at a height of 200–250ft above the ocean. Approaching the target at high speed, the aircraft flew parallel to the ship and dropped its bombs as it approached. The weapons, armed with five second time fuzes, hit the water and skipped like flat stones over its surface. They either skipped into the ship and exploded on impact, or sank in the water alongside the vessel, detonating next to the hull and “mining” it.
Alternatively, the ordnance could be held until the bomber was overhead the ship at mast top height, at which point the bomb (fitted with a delayed action fuze so as to ensure the aircraft had enough time to avoid being engulfed in the subsequent blast) was dropped and penetrated deep into the ship before exploding. Either technique significantly increased the hit percentage, but also the risk of being struck by light antiaircraft fire.
Maj Benn demonstrated the technique’s effectiveness in the B-17, even using it on combat missions. Kenney realized other aircraft in his inventory, especially Gunn’s strafer A-20s and B-25s, were better suited to using skip and mast top bombing attacks. Twin engined aircraft were more agile than four engined B-17s, and more expendable. Additionally, the nose guns in Havocs and Mitchells solved a major problem with low level attacks.
The heavy slugs fired by the 0.50 cal. machine guns cleared the ships’ decks of personnel, thus suppressing light antiaircraft fire. They also penetrated the decks and gun turrets of the IJN destroyers, wreaking havoc inside the vessels. While a Japanese destroyer’s 127mm guns were normally ineffective against aircraft flying at medium to high altitude, they were capable of knocking down a twin engined bomber flying straight at the destroyer at low level. But these guns were silenced, along with the vessel’s more exposed light antiaircraft guns, by a well executed strafing attack.
Kenney soon had aircraft from the 3rd BG, especially strafer equipped A-20s of the 89th BS and B-25s of the 90th BS, practicing skip bombing against the wreck of SS Pruth, a 4,700 ton steamer that had run aground on Nateara Reef near Port Moresby during a storm in January 1924. While practicing, two aircraft were damaged by flying debris from bomb blasts, and a third crashed after colliding with the wreck’s mast. Hard practice was necessary to master both demanding techniques.
It paid off. By the end of February, pilots had become proficient. Often, they combined the techniques, skip bombing with the first two bombs dropped and using mast top bombing for the final two, sometimes getting four hits with four bombs. In the end, most crews opted for mast top bombing over skip bombing. It was easier to master, and the results were almost identical. Kenney only needed a suitable opportunity to field test his bombers.
Over the first two months of 1943, squadrons perfected these tactics. Then, in early March, Japan tried to reinforce their garrison in Lae, New Guinea, with a 16-ship convoy – eight transports guarded by eight destroyers. The Fifth Air Force pounced on the convoy in the Bismarck Sea. By Mar. 5 all eight transports and four destroyers had been sunk.
B-25 Mitchell vs Japanese Destroyer, Battle of the Bismarck Sea 1943 is published by Osprey Publishing and is available to order here.
Photo credit: Jim Laurier via Osprey Publishing and Rare Historical Photos
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