North American B-25 Mitchell

History

Text about the development.

Versions.

North American B-25.

Of this, in fact pre production version just twenty-five examples were built, the first being delivered in February 1941.

These aircraft were armed with three .303 inch machine-guns, one in the nose, one through the floor and one pointing through the back plus one .50 machine-gun in the tail.

The first nine examples had a more or less straight wing, slightly pointing upwards. This configuration caused instability, so a new wing configuration in which the part of the wing pointing outwards from the engine was placed under an angle of zero degrees., the well known gull wing of the Mitchell . USAAC serials were 40-2165  till 40-2188

North American B-25A.

An improved version with armouring, an improved arrangement of machine-gun in the tail and furthermore self sealing fuel tanks in the wings Some forty examples of this version were built, USAAC serials  40-2189 till 40-2228.

North American B-25B.

The machine-gun in the tail was removed, the machine-gun arrangement on the back and belly position were replaced by a manned turret with two .50 inch machine-guns and a retractable, remote turret with also two .50 machine-guns,  in the lower position. 124 examples were built, with USAAC serial 40-2229 - 40-2348. The RAF received some of this series under the designation Mitchell Mk.I

Well known is the fact that the model B-25C and B-25D were virtually equal. The C was built in the North American-factory at Inglewood, the B-25D was built in the factory at Kansas City. The latter factory was set up by the US government in order to keep up the war production. Several production blocks which were distinguished by several modifications were built. In fact these types could be identified because of the slightly different wave between the Olive Drab and the Neutral Grey: Inglewood produced Mitchells had somewhat less proportional wave than the Kansas City produced examples

North American B-25C.

The first NEIAF order for 163 B-25Cs, designation NA-82 was signed September 24, 1940.
The B-25C resembled the earlier B-25B and differed in the R-2600-13 Double Cyclone engines with a Holley 1685HA carburettor, which replaced the Bendix Stromberg PD-13E-2 units. These were easier to maintain, but requested a careful de-icing. Further de-icing systems were added, a Stewart-Warner cockpit heating and the electrical system was now 24 Volt.

The armament was initially equal to the armament of the B-25B, to know one single 0.30-inch nose mounted machine gun two 0.50-inch machine guns in the dorsal turret and two 0.50-inch machine guns in a retractable ventral Bendix turret. Often this ventral turret was removed.
Another difference was the new type tail skid, this became a massive rubber skid used on all types to be produced. Also the single exhaust of each engine was shortened.

• From B-25C Fisc. Year no. 41-13176 the nose armament was enforced and became two .303 inch machine guns. A small transparent dorsal blister for the navigator was added from fisc. year no. 41-12817 Also the type of turret was changed in Bendix Amplidyne and an extra 304 US gallon external wing mounted fuel tanks could be used. (I have never seen photos of B-25s using these tanks.)
• B-25C-1 a wing mounted bomb rack was introduced also a torpedo could be used.
• B-25C-5 the 0.30-inch machine gun was replaced with a moveable 0.50-inch machine gun and a fixed 0.50-inch machine gun star board. Also the single exhaust was replaced with several shorter ones, just pointing out of the cowling.
• B-25C-10 mainly internal modifications.
• B-25C-15 Improved Clayton "S"-like flame damping exhaust for each cylinder was used. These exhausts were used on every succeeding B-25 model. Also an emergency system for the hydraulic landing gear was used.

North American B-25D.

The General Motors factory at Kansas City was leased by the North American Aviation in order to built the B-25 Mitchell. The Fisher Body Division of General Motors Corporation was the main contractor. The first order for the delivery of 1200 B-25Ds (NA-82) was signed June 28, 1941. North American/Inglewood produced the first parts for the first 100 B-25Ds.
The first B-25D's were delivered in February 1942. The B-25D was virtually identical to the B-25C and many modifications of the B-25D were parallel with the modifications of the B-25C.

• B-25D 41-29648 till 41-29797 two .303 inch machine guns were mounted, later replaced with two .50 machine guns.
• B-25D-10 mainly internal modifications were introduced.
• B-25D-15 Fisc year no. 41-30353 and on the improved Clayton "S"-like exhaust were introduced.
• B-25D-20 Fisc. Year no. 41-30533 modifications like clear vision wind screen; self sealing 230 gallon tank in bomb bay (every second aircraft); armour plating for the co pilot were added.
• B-25D-25, fisc. year no. 42-87138 and on a movable oxygen unit.
• B-25D-30 further “winterization” modifications and de-icing of the windscreen was added.
• The last version was B-25D-35.

North American B-25J

The B-25J (NA-108) was the last version to be produced. This model was built in the largest numbers. This model was produced in North American’s factory at Kansas City only. For a while both model B-25D and B-25J were built together. The first B-25J was delivered in December 1943; the last B-25D was delivered in March 1944. The medium bomber function of the B-25 returned with armament in the tail, turret, nose and blisters on both sides. Bomb racks and doors were electrically managed.
For the tailgunner heating was added. Three 1000 pound bombs could be carried and also two 1600-pound armour penetrating bombs could be carried. Also six 325 pound depth bombs could be carried under the wings.
The transparent nose section could be replaced with a solid nose with eight fixed 0.50-inch machine guns. Aircraft with this modification were designated B-25J-11, -17, -22, -27, -32, of -37, depending of the production block.

• B-25J-1 From fisc. year no. 43-4019 and on the provision for the 2000 pound bomb was deleted; these proofed to be in sufficient.
• B-25J-5 besides several internal modifications, de icing of the wind screen and gun-blast arrestors for the turret and blisters were added.
• B-25J-10 provision for wing mounted bomb racks were added; the electrical managed bomb racks and heating of the side armament was insufficient and removed.
• B-25J-15 Main modifications: Movable armament was equipped with new direction finders.
  The NEIAF Used B-25J-15s: N5-232 till N5-N5-241. N5-232 and N5-235 were handed over to the RAAF.
• B-25J-20 a second fixed 0.50-inch machine gun was installed in the nose. The moveable gun was relocated at a 4 inches higher position. The floor in the nose was armored. The canopy of the turret was strengthened and a hydraulic emergency brake was added.
  The NEIAF used B-25J-20s: N5-242 till N5-249.
• B-25J-25 Both pilot seats were armored; From fisc. year no 44-30111 armored deflector on the fuselage were used to prevent damage of the own plane by the gunner in the turrets.
  The NEIAF used B-25J-25s: N5-250 till N5-258 and N5-266.
• B-25J-30 the steel exhausts of cylinders 1, 7, and 9 were replaced with stainless steel examples. From fisc. year no 44-31311 an electrical bomb loading system was added. From fisc.year no. 44-31338 a provision for wing mounted rockets (T-64 rocket launchers for eight 5” HVAR (high-velocity aircraft rockets) was added. Later a provision to carry glide bombs was added.
  The NEIAF used B-25J-30s: N5-259 till N5-265.
• B-25J block 35 A provision for carrying mines was added. The transparent nose could be replaced with a solid nose with eight machine guns. The NEIAF modified several B-25J with this nose. These were designated as "B-25K".