Tuesday, February 17, 2015

Dive-bombers – a comparison

The Aichi D3A (Val) dive-bomber entered service in 1940. In many ways similar to the German JU-87 Stuka, it was Japan’s top naval dive-bomber of the war and the most successful Axis warplane against Allied ships. An all-metal, low-winged monoplane with fixed landing gear, it was comparable to but somewhat lighter (at 8,047 pounds) than the Douglas SBD Dauntless of the United States (see below). The D3A (1,495 produced) was capable of 240 mph and a range of 915 miles. It was armed with three machine guns and carried one 551-pound bomb under the fuselage and two 132-pound bombs under the wings. A total of 126 Vals took part in the Pearl Harbor strike. Vals served throughout the war and were used at war’s end as kamikaze aircraft.

The United States lead the field, both in doctrine and equipment. The U.S. Marine Corps first used dive-bombers in action in Nicaragua in July 1927. By 1931, the U.S. Navy’s experiments with the Curtis Hawk caught the attention of the Japanese. They ordered two He50s from the German manufacturer Heinkel for their own tests. Within the next ten years both the U.S. and the Japanese navies had developed the Douglas SBD Dauntless (U.S. Army Air Forces designation: A-24) and the Aichi D3A Type 99 Val variants, respectively, that would serve each during much of the war. During the critical carrier battles of 1942 these two types of dive-bombers accounted for 70 percent of all ships sunk.

Most dive-bombers had similar specialized features. Steep dive angles were required both to ensure accuracy and to offer the minimal exposure to antiaircraft fire. In early models, however, the angle caused the bomb to damage or destroy the plane’s propeller as it left the aircraft. Bomb displacing gear (called a “fork” or “crutch”)—first added by the United States in 1931—threw the bomb clear of the propeller. Stability was paramount for accurate dive-bombing, but the slipstream from the wings buffeted the tail; therefore, dive brakes (perforated flaps along the wings’ trailing edge) were added.

The Dauntless was the standard U.S. Navy dive-bomber in 1941. It had a top speed of 250 mph and a loaded range of 1,300 miles. Dauntless variants included the scout (with 100- and 500-pound bomb combinations) and the bomber (one 1,000-pound bomb). The Val carried one 550-pound bomb at 240 mph to a range of 1,250 miles (five hours’ endurance), and it sank more Allied ships during World War II than any other Axis aircraft. It remained in production until the end of the war. Both the Dauntless and the Val had a crew of two and were difficult to shoot down when bombless, although neither had self-sealing fuel tanks. Midway through the war both navies fielded new but unsatisfactory dive-bombers, the Curtiss SB2C Helldiver and the Yokusaka D4Y Judy, respectively.

The Helldiver replaced the Dauntless, coming to the fleet in 1943. But its structural problems required major modifications, so it deployed in large numbers only in mid-1944. The Helldiver had an internal bomb bay and flew 20 mph faster than the Dauntless, but it carried the same bomb load; however, it was much harder to fly and maintain. Overall, it did not represent much of an improvement over the Dauntless. The Judy mounted the Japanese version of the engine which powered Messerschmidt fighters. Flying at 360 mph, it was by far the world’s fastest dive-bomber. Like the Helldiver, however, it had reliability problems. It was underarmored and also lacked self-sealing fuel tanks. The Judy never completely replaced the Val, anymore than the Helldiver replaced the venerable Dauntless.

Doctrinally, dive-bombers of both navies usually worked in close coordination with torpedo bombers and in many cases with level bombers and even high-altitude bombers. Because the defensive measures that ships took against each type of attacking aircraft were different, this combined-arms approach was very effective.

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