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. 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 co-pilot 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. B-25 fuselage arrangement
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, eight-gun nose.
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 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 in the bomb bay. 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. Armor Protection - Location of emergency equipment
The -35 production block introduced provisions for the carrying and laying of aerial mines.
Some of the B-25Js were assigned to training units, but most were issued to units in action in the Southwest Pacific. The first B-25Js arrived at Townsville, Australia and Nadzab, New Guinea 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 theater, 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 for the bombardier could be replaced by a factory built solid gun 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 one of 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. B-25 forward armament
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 108-24196/24430
43-27473/27792 North American B-25J-1 Mitchell c/n 108-34486/34805
43-27793/28112 North American B-25J-5 Mitchell c/n 108-34806/35125
43-28113/28222 North American B-25J-10/11 Mitchell c/n 108-35126/35235
43-35946/36245 North American B-25J-10/11 Mitchell c/n 108-35236/35535
44-28711/29110 North American B-25J-15/17 Mitchell c/n 108-31986/32385
44-29111/29910 North American B-25J-20/22 Mitchell c/n 108-32386/33185
44-30748 North American B-25J-25/25 Mitchell c/n 108-34023 - "Heavenly Body"
44-29911/30910 North American B-25J-25/27 Mitchell c/n 108-33186/34185
44-30911/31510 North American B-25J-30/32 Mitchell c/n 108-36986/37585
44-86692/86891 North American B-25J-30/32 Mitchell c/n 108-47446/47645
44-86892/86897 North American B-25J-35/37 Mitchell c/n 108-47646/47651
45-8801/9242 North American B-25J-35/37 Mitchell c/n 108-47652/47750
45-9000/9242 canceled contract for B-25J-35 Mitchell