In early 1938 the US Army Air Corps put forth a specification for a new medium bomber, an aircraft capable of carrying a 1,200lb payload with a speed in excess of 200mph and with a range of at least 1,200 miles. In 1939 the USAAC upped the requirements with specifications for a medium bomber with a speed of 300mph, range of 1200 miles and a payload of 2,400lbs. In September of the same year, The Army Air Corps ordered the North American NA-62, the B-25, along with another 2 engine aircraft, the Martin B-26 Marauder.

Through the initial production and flight, it was discovered that the wing of the B-25 required a redesign due to an in-flight stability issue. The outer wing was changed from having a constant dihedral to an anhedral, or gull wing, configuration which solved the problem. Other relatively minor changes were made during the design & development of the B-25 through 1940 and 1941.

The US military began operating both the B-25A and B-25B, though with the need for changes in the aircraft for combat purposes and, by the end of 1942, North American Aviation was producing both the B-25C and B-25D at two different aircraft factories. NAA was also working on developing a cannon equipped version of the bomber known as the B-25G with further developments in the works for models of the Mitchell, including the H, J and J2 models.

Early models of the B-25 were fitted with the Wright R-2600-9 radial engines offering 1350hp in each engine. Aircraft defences consisted of just three .30 calibre machine guns with one in the nose, the waist and another in, what was referred to as, the ventral position. There was also a .50 calibre machine gun mounted in the tail, offering better tail-end protection. The payload of the Mitchell was also increased to 3,600lbs.

The B-25A, the first of the combat versions, saw a production of just 40 aircraft before the B-25B was brought online with slightly better armament with 120 aircraft built. Though the USAAC operated most of these aircraft, the Royal Air Force also operated several B-25Bs, referred to as the Mitchell Mk I. Though the B-25 saw operational service in the European Theatre of war, most Mitchells saw service in the Pacific Theatre of war.

In fact, one of the most famous American bombing raids took place in the Pacific Theatre of War when the B-25B was used to attack the Japanese mainland. Sixteen B-25Bs were launched from the aircraft carrier, USS Hornet, after months of arduous training. Known as the "Doolittle Raid" or "Tokyo Raid," it was launched in April of 1942 and was lead by Lieutenant Colonel Jimmy Doolittle, with each bomber carrying 5 crew members. They were to attack assorted industrial targets and then continue on to land in China.

Though these attacks didn't cause an immense amount of damage, there were in excess of 400 people injured with an additional 50 killed. The attacks, however, did boost US morale and proved that the Japanese mainland was vulnerable to attack. Of the sixteen B-25s, all but a single bomber were destroyed in crashes, with the single surviving aircraft having managed to land in Vladivostok, Soviet Union. Of the aircraft crews, 14 crews eventually managed to return to the United States or to the US forces. Eight crew members were captured by the Japanese forces of which 3 were eventually executed by the Japanese. Lt. Col. Doolittle felt that, due to the loss of aircraft, he would be facing court-martial upon his return to the States. In fact, the opposite happened and he was awarded the US Medal of Honor and was promoted up two ranks to Brigadier General.

Next week we'll continue our look at the North American B-25 Mitchell and further variants, including updated armament and engines and the different roles the Mitchell flew in. It was a workhorse aircraft and served with different air forces around the world with great distinction.