On the contrary; it was the very same old 75 mm M-4 field cannon used to rout the Germans in WW1! A few months before the incident, Colonel Paul Gunn of the US Fifth Air Force in Australia, had experimented with the installation of a 20 mm cannon in the nose of a B-25. Colonel Gunn, abetted by a North American Aviation Company Tech Rep named Jack Fox, sent the idea to North American in Inglewood, California where it was promptly taken a step further and worked into the installation of the 75 mm cannon.

Then came the installation of the 75 mm cannon. It required a crewman to load, fire and extract the casing. And when it fired it felt like the aircraft had "hit a brick wall", but with its 2.95 inch (75 mm) projectile, it could turn a tank into scrap metal and punch very large holes in Japanese destroyers and barges at a range of nearly 2 miles. The Japanese paid dearly for the ideas of Kenney and the ingenuity of Gunn.

The result from North American was a dramatically updated NA-40, redesignated the NA-62. The design was much more streamlined with the rear of the "greenhouse" canopy neatly faired into the fuselage (instead of the "upside down bathtub" of the NA-40), forming a straight line from the top of the windshield to the tail assembly. On August 10, the design was accepted by the USAAC as the B-25 and ordered into production straight off the drawing board, something not often done with new aircraft. The B-25 was fitted with two turbo supercharged Wright R-2600 Cyclone radial engines and though the dash numbers changed and modifications were made to it, the supercharged R-2600 Cyclone was standard through the final production model which was the B-25J.

The B-25A was a bit more suited for combat than its predecessor, having self sealing fuel tanks and crew armor. However, most of the "A"s never saw combat but were used by the Army for coastal patrol and reconnaissance. Though the "A" had more armor, it was considered obsolete in a very short time because of its lack of provisions for self defense. A single thirty caliber (7.62 mm) machine gun was located at the waist and could be plugged into a ball socket on either side, another .30 cal. (7.62 mm) in the nose and one fired from a sockets in the top of the fuselage. Because of the opinion that most attacks would come from the rear, the prone tail gunner operated a .50 cal. (12.7 mm) machine gun. Forty B-25As were built by the end of production in August, 1941.

The Doolittle raid was carried out by sixteen B-25B aircraft. The "B" was built with the advantage of a degree of combat experience. Dorsal and ventral gun turrets, each housing twin .50 cal. (12.7 mm) M-2 Browning machine guns were installed just behind the bomb bay. The .30 cal. (7.62 mm) was retained in the nose position. The tail gunners position was eliminated and an observers station installed. Although the turrets adversely affected the top speed of the B, firepower was greatly improved.

The B-25D was identical to the "C", the only difference being the "D" was manufactured at the North American plant in Kansas City instead of the plant in Inglewood, California.

There was only one copy each of the "E" and "F" models. They were both taken directly off the "C" production line and used solely for the purpose of testing new anteing and de-icing equipment.

The first B-25G was serial #41-13296 which was taken off the "C" line and modified for the 75 mm M-4 cannon installation. The greenhouse nose was removed and replaced with a solid nose equipped with a pair of fixed, forward firing M-2 machine guns and the 75 mm M-4 cannon which ran under the pilots seat. Behind the pilot a gunner loaded, fired and extracted the empty shell casings. Twenty-one rounds were carried for the cannon. Armor was added to protect the gunner and the cannon rounds. Five of the "C"s were modified to the "G" configuration for testing before the production line started turning out "G"s. About 1,400 B-25Gs were produced.

The B-25J reverted to the greenhouse bombardier nose of the "C" model, but with far more firepower. Some variants had as many as 14 forward firing M-2 machine guns in front and four more at various other stations in the craft. The 75mm cannon was removed and a bombardier was again added as the sixth crewman. B-25Js were by far the largest production run of the Mitchell bomber with more than 4,300 copies delivered before the war ended and production lines of the B-25 were shut down for good.

Other aircraft were larger, faster, "prettier" and produced in greater quantities. But none could surpass the colorful career of the North American B-25 Mitchell bomber.