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B-25 Mitchell

The North American B-25 Mitchell, a twin-engine bomber that became standard equipment for the Allied air forces in World War II, was perhaps the most versatile aircraft of the war. It became the most heavily armed airplane in the world, was used for high- and low-level bombing, strafing, photoreconnaissance, submarine patrol, and even as a fighter and was distinguished as the aircraft that completed the historic raid over Tokyo in 1942. James Doolittle led a B-25 squadron on a daring post-Pearl Harbor retaliatory raid over Tokyo in April 1942. It required 8,500 original drawings and 195,000 engineering man-hours to produce the first one, but nearly 10,000 were produced from late 1939, when the contract was awarded to North American Aviation, through 1945. Named for famed airpower pioneer Brigadier General William “Billy” Mitchell, it was a twin-tail, mid-wing land monoplane powered by two 1,700-horsepower Wright Cyclone engines. Normal bomb capacity was 5,000 pounds (2268 kilograms). Some versions carried 75 mm cannon, machine guns and added firepower of 13 .50-caliber guns in the conventional bombardier's compartment. One version carried eight .50-caliber guns in the nose in an arrangement that provided 14 forward-firing guns. North American Mitchell began development of the B-25 Mitchell in the mid-1930s as a transport aircraft. The company modified the aircraft in 1939 to serve as a medium-range bomber in 1939. There was such a desperate need for this type of bomber that North American did not build any experimental or prototype versions during the development. Changes to the basic design were incorporated into aircraft on the production line or post-production modification centers. A significant modification was the switch from angled wings to the "gull wing" design to improve stabilization. The military received the first B-25s in February 1941. The US, and several of its allies, used the B-25s in every combat area of the war for mid-level bombing and low-altitude raids. The B-25C, powered by two Wright R-2600-13 radial engines, was the first mass-produced B-25. It included deicing equipment, a window in the nose, and nose armament. In 1942 a B-26C was modified to flight test deicing and anti-icing equipment. The aircraft, dubbed "the Flamin' Maimie," routed engine exhaust gases to heat exchangers that circulated the hot gas throughout the leading and trailing edges of the wings and tail.

B-25 Mitchell - Operations

Just as Pappy Gunn and his experimental workshop at the 81st Depot Repair Squadron in Townsville, Australia, had modified the A-20, so did they add a series of .50-caliber machine guns to the B-25 bomber around November 1942. Again, the idea was to add an extra offensive dimension to the aircraft, and the process itself says something about the “we’ll try anything” attitude of Gunn and his men.

In November Kenney had sent word to Pappy Gunn to pull the bombardier and everything else out of the nose of a B-25 and fill the space with .50-caliber machine guns. For good measure, more guns were to be strapped around the nose to give as much forward firepower as the plane could carry. If it still flew, the Fifth would have a low level bomber which could clear the decks of a Japanese ship as it made its run. With this “commerce destroyer,” the aerial blockade could be enforced anywhere within their range. It was the morning of November 29 when Kenney first went to look over the job.

A package of four guns, similar to those on the A-20, fitted neatly in the nose, and two more were being mounted in packages on each side of the fuselage just under the cabin. Three more were going underneath the fuselage, but the ammunition feed was causing difficulties, and it seemed they would have to be discarded.

Pappy Gunn reported that firing the guns had popped some rivets, but that could be cured with longer blast tubes and stiffer mounts. Kenney thought the plane looked nose-heavy, and asked Gunn about the center of gravity. Pappy’s lined face was impassive: “Oh, the C.G. Hell, we threw that away to lighten the ship.”

Kenney returned about ten days later, and since the aircraft was still nose-heavy, it was decided to move the gun packages on each side of the fuselage back about three feet. They were still popping rivets even though the fuselage had been stiffened with steel plates, so felt was put between the plates and the skin to soak up the shock. However, the felt dried hard after it was wet and the vibration was tremendous. Sponge rubber was the answer. Every time the troublesome bottom guns were fired the door that folded up behind the nosewheel fell off, so Kenney settled for the four nose guns, the two on each side, and wanted the top turret guns fixed so they could be locked to fire forward. He told Gunn to fire twenty thousand rounds through the installation and if the plane was still holding together he would put together a squadron.

B-25s in the SWPA had their tail guns and belly turrets removed. After all, the use of low-level tactics eliminated the need to defend against fighter attacks from below. The new forward firepower had occasion to make up for the loss of such defensive fire: “We added 50 cals. in there. (Most of them came out of cracked up P-40’s.) . . . That is essential because the Japanese pilots figure things out very rapidly. They found the most vulnerable spot was a frontal attack. They would come right in. After the 50 cals. with tracers were fired out a few times, their aggressiveness fell off a little bit.”

Crews found, just as prewar tactics had suggested, that fire from their new guns kept the enemy under cover, away from their antiaircraft weapons, and generally minimized the danger of the crews themselves getting shot.