[Curly1]

Use as a gunship[edit]Because of the urgent need for hard-hitting strafer aircraft, a version dubbed the B-25G was developed, in which the standard-length transparent nose and the bombardier were replaced by a shorter solid nose containing two fixed .50 in (12.7 mm) machine guns and a 75 mm (2.95 in) M4 cannon,[2] one of the largest weapons fitted to an aircraft, similar to the experimental British Mosquito Mk. XVIII, and German Ju 88P heavy cannon carrying aircraft. The cannon was manually loaded and serviced by the navigator, who was able to perform these operations without leaving his crew station just behind the pilot. This was possible due to the shorter nose of the G-model and the length of the M4, which allowed the breech to extend into the navigator's compartment.

The B-25G's successor, the B-25H, had even more firepower. The M4 gun was replaced by the lighter T13E1,[2] designed specifically for the aircraft. The 75 mm (2.95 in) gun fired at a muzzle velocity of 2,362 ft/s (about 720 m/s). Due to its low rate of fire (approximately four rounds could be fired in a single strafing run) and relative ineffectiveness against ground targets, as well as substantial recoil, the 75 mm (2.95 in) gun was sometimes removed from both G and H models and replaced with two additional .50 in (12.7 mm) machine guns as a field modification.[3]

Besides that, the -H normally mounted four fixed forward-firing .50 (12.7 mm) machine guns in the nose, four more fixed ones in forward-firing cheek blisters, two more in the manned dorsal turret, one each in a pair of new waist positions, and a final pair in a new tail gunner's position. Company promotional material bragged the B-25H could "bring to bear 10 machine guns coming and four going, in addition to the 75 mm cannon, a brace of eight rockets and 3,000 lb (1,360 kg) of bombs."[4]

The B-25H also featured a redesigned cockpit area, required by the dorsal turret having been relocated forward to the navigator's compartment - just aft of the cockpit and just ahead of the leading edge wing roots, thus requiring the addition of the waist and tail gun positions - and a heavily modified cockpit designed to be operated by a single pilot, the co-pilot's station and controls deleted, and the seat cut down and used by the navigator/cannoneer, the radio operator being moved to the aft compartment, operating the waist guns.[5] A total of 405 B-25Gs and 1000 B-25Hs were built,[2] the 248 of the latter being used by Navy as PBJ-1H.

The final, and the most built,[2] version of the Mitchell, the B-25J, looked much like the earlier B, C and D, having reverted to the longer, glazed bombardier's nose, but with the -H version's relocated-forward dorsal manned turret. The less-than-successful 75 mm (2.95 in) cannon was deleted. Instead, 800 of this version were built with a solid nose containing eight .50 (12.7 mm) machine guns, while other J-models featured the earlier "greenhouse" style nose containing the bombardier's position.[6]

Regardless of the nose style used, all J-models also included four .50 in (12.7 mm) light-barrel Browning AN/M2 guns in a pair of "fuselage package", flank-mount conformal gun pods each containing two Browning M2s, located directly beneath the pilot's and co-pilot's compartment along the external sides of the cockpit, with the co-pilot's seat and dual flight controls restored to their previous cockpit locations. The solid-nose B-25J variant carried a total of 18 .50 in (12.7 mm) light-barrel AN/M2 Browning M2 machine guns: eight in the nose, four in the flank-mount conformal gun pod packages, two in the dorsal turret, one each in the pair of waist positions, and a pair in the tail - with fourteen of the guns either aimed directly forward, or aimable to fire directly forward for strafing missions. No other main series production bomber of World War II carried as many guns.[6]

The first 555 B-25Js (the B-25J-1-NC production block) were delivered without the fuselage package guns, because it was discovered that muzzle blast from these guns was causing severe stress in the fuselage; this problem was cured with heavier fuselage skin patches. Although later production runs returned these fuselage package guns to the aircraft, they were often removed as a field modification for the same reason.[6] The later B-25J was additionally armed with eight 5 in (130 mm) high-velocity aircraft rockets (HVAR).[2] In all, 4,318 B-25Js were built.