The B-25J (NA-108) was the final production version of the Mitchell. It was also the version of the Mitchell to be built in the largest numbers, a total of 4318 being built. It was manufactured exclusively at North American's Kansas City plant, the Inglewood plant having switched over to the manufacture of the P-51 Mustang fighter after the last B-25H had been delivered.
Kansas City briefly built both the B-25D and J at the same time, the first J being accepted in December 1943 and the last D in March of 1944.
The B-25J returned to its primary function as medium bomber, and reverted to the transparent, bombardier-equipped nose of the earlier B-25C and D. The tail gun position with the deeper rear fuselage, the bay-window mounted waist guns, and the forward-mounted dorsal turret that had been introduced on the B-25H were all retained on the B-25J. The blister gun packs on the sides of the forward fuselage of the later versions of the B-25H were also retained. However, the copilot position (which had been omitted on the B-25H) was restored. The crew was now six--pilot, co-pilot, navigator/bombardier/gunner, turret gunner/engineer, radio operator/waist gunner, and tail gunner. The bomb racks and bomb bay doors were now all electrically-operated. A 50,000 BTU surface combustion heater was provided at the waist gun station. Provision was made to carry three 1000 pound bombs rather than just two. Alternatively, two 1600-pound armor-piercing bombs could be carried. Provisions were made for the carrying of six 325-pound depth charges on underwing racks.
The first B-25J (43-3780) took off on its first flight in October 1943, piloted by Joe Barton. The first USAAF acceptance took place before the end of the year.
The B-25J was built in eight main production blocks (-1, -5, -10, -15, -20, -25, -30, -35), with different suffix numbers being allocated to significant modifications, including -11, -17, -22, -27, -32, and -37. Many of these modifications involved the replacement of the transparent nose by a solid nose armed with eight fixed machine guns.
Beginning with the 151st B-25J-1 (43-4019), provisions for the carrying of a single 2000-pound bomb were deleted. As it turned out, the 2000-pound bomb was only rarely carried during actual combat, and the bulky and restrictive shackles for the 2000-pound bomb took up a lot of space in the bomb bay. This enabled a normal offensive load of two 1600-lb or three 1000-lb bombs to be carried internally, plus combinations of smaller bombs of various types, including 20-pound parafrags.
The -5 production block introduced a revised braking system control cable. The N-3C gunsight replaced the N-3B sight and A-1 bombing head. De-icing windshield panels were installed, and gun-blast arrestors were installed on top turret guns and on side fuselage blister guns.
The -10 production block introduced the mounting lugs and controls for underwing bombs. Electric bomb racks were provided. The heaters at the waist gun positions were found to be inefficient and were removed.
The -15 production block had N-8A optical gunsights installed on the flexible waist guns. Provisions for ring and bead sights were provided for the flexible nose gun.
The -20 production block introduced some revisions to the cabin heating system with a 50,000 BTU/hour heater. A second 0.50-inch fixed machine gun was installed in the nose. The flexible nose gun was relocated 4 inches higher. Additional armor protection was provided in the floor of the nose for the bombardier. The top turret canopy was reinforced for greater strength, and a hydraulic emergency brake system was incorporated. Beginning with 44-29304, a change was made to the Holley 1685RB carburetor.
The -25 production block introduced new types of armored seats for both pilots. Beginning with 44-30111, armored plate deflectors were added to the upper fuselage to prevent the upper turret gunner from inadvertently firing his guns into the structure of his own plane, especially into the raised cupola where the tail gunner sat. Beginning with 44-30309 and throughout the -25 production block, provisions were made for the mounting of a chemical tank on an underwing bomb rack.
On production block -30, stainless steel "S"-shaped exhaust stacks replaced the enameled 1020 steel stacks on cylinders 1, 7, and 9. Effective with serial number 44-31111, provisions were made for the mounting of a chemical tank on an underwing bomb rack. Provisions for a type C-6 electric bomb hoist were made effective with 44-31311. Provisions were made for the carrying of wing-mounted T-64 zero-length rocket launchers beginning with 44-31338. These launchers could carry up to eight five-inch high-velocity aircraft rockets (HVAR). Beginning with 44-31491, a K-10 computing gunsight was provided for the gunner in the tail turret, and M-8A gun mounts were provided for the tail guns. Provisions for the mounting of glide bombs suspended underneath the fuselage were added beginning with 44-86692. In addition, a special cockpit sight and release controls for the glide bomb were provided. An N-9B bombsight was installed beginning with 44-86793. Beginning with 44-86799, the rudder control cables were rerouted.
The -35 production block introduced provisions for the carrying and laying of aerial mines.
Some of the B-25Js ended up with training units, but most were issued to units in action in the Southwest Pacific. The first B-25Js arrived at Townsville and Nadzab depots in the summer of 1944. They were issued to the 38th Bombardment Group. The 345th BG received its B-25Js in September. Despite volume production, it was hard to meet the demand, and the 42nd Bombardment Group did not get its B-25Js to replace its aging C and D models until late 1944.
In the Mediterranean theatre, the B-25J was issued to operational bomb groups on an as-required basis. In April 1944, the 310th Bombardment Group based on Corsica received its first B-25Js. The remaining groups in the 57th Bombardment wing of the 12th Air Force transitioned to the B-25J throughout the remainder of 1944.
The US Marine Corps ordered 255 B-25Js under the designation PBJ-1J.
The transparent nose with its bombardier could be replaced at the factory by a solid nose that was equipped with eight 0.50-inch machine guns. With this modification, the aircraft was designated as B-25J-11, -17, -22, -27, -32, or -37, depending on which production block the modification took place. With its maximum armament of eighteen guns, the solid-nosed B-25J was the most heavily-armed attack aircraft in the Allied arsenal. Sometimes, however, the package guns on the sides of the fuselage were deleted, the remaining fourteen guns being more than enough forward-directed firepower.
The last B-25J was delivered to the USAAF in August of 1945. The day after the war in the Pacific ended, the Kansas City plant was closed.
43-3870/4104 North American B-25J-1 Mitchell c/n 108-24196/108-22430 43-27473/27792 North American B-25J-1 Mitchell c/n 108-34486/108-34805 43-27793/28112 North American B-25J-5 Mitchell c/n 108-34806/108-35125 43-28113/28222 North American B-25J-10/11 Mitchell c/n 108-35126/108-35235 43-35946/36245 North American B-25J-10/11 Mitchell c/n 108-35236/108-35535 44-28711/29110 North American B-25J-15/17 Mitchell c/n 108-31986/108-32385 44-29111/29910 North American B-25J-20/22 Mitchell c/n 108-32386/108-33185 44-29911/30910 North American B-25J-25/27 Mitchell c/n 108-33186/108-34185 44-30911/31510 North American B-25J-30/32 Mitchell 30911/31110 c/n 108-34186/108-34385 31111/31510 c/n 108-37186/108-37585 44-86692/86891 North American B-25J-30/32 Mitchell c/n 108-47446/108-47645 44-86892/86897 North American B-25J-35/37 Mitchell c/n 108-47646/108-47651 45-8801/9242 North American B-25J-35/37 Mitchell c/n 108-47652/108-47750 45-9000/9242 cancelled contract for B-25J-35 Mitchell
Engines: Two Wright R-2600-13 Double Cyclone fourteen-cylinder air-cooled radials, rated at 1700 hp each for takeoff and 1500 hp at 2400 rpm. Equipped with Holley 1685HA carburetors. Performance: Maximum speed 275 mph at 15,000 feet. 230 mph cruising speed. Initial climb rate 1110 feet per minute. An altitude of 15,000 feet could be reached in 19 minutes. Service ceiling 24,000 feet. Range 1275 miles with 3200 pounds of bombs. Ferry range 2700 miles. Dimensions: Wingspan 67 feet 6.7 inches, length 53 feet 5.75 inches (bomber version), height 16 feet 4.2 inches, wing area 610 square feet. Weights: 21,100 pounds empty, 33,000 pounds normal loaded, 35,000 pounds gross, 41,800 pounds maximum overload. Fuel: The fuel capacity consisted of four tanks in the inner wing panels, with a total capacity of 670 US gallons. In addition, 304 US gallons of fuel could be carried in auxiliary tanks in the outboard wing panels, for a normal total fuel load of 974 US gallons. A 515-gallon tank could be installed in the bomb bay for ferrying purposes, 125 gallons of fuel could be carried in side waist positions, a 215-gallon self-sealing fuel tank installed in the top of the bomb bay, and provisions could be made for a droppable 335-gallon metal bomb-bay fuel tank. Armament: Medium bomber version: One flexible 0.50-inch machine gun in nose, 300 rounds. One fixed 0.50-inch machine gun in nose, 300 rounds. Beginning with B-25J-20, a second fixed 0.50-inch gun was added in the nose. Strafer version: Eight 0.50-inch machine guns in the nose with 400 rpg. All versions: Two 0.50-inch machine guns in individual blisters on each side of the forward fuselage with 400 rpg. Two 0.50-inch machine guns in top turret, 400 rpg. Two 0.50-inch machine guns in waist position, 200 rpg. Two 0.50-inch machine guns in tail turret, 600 rpg. Normal bomb load was 3000 pounds, but a maximum bombload of 4000 pounds could be carried on short-range missions. Some had underwing racks for eight 5-inch high velocity aircraft rockets (HVARs).