Doolittle raider B-25B 40-2242 aboard USS Hornet
The development and deployment of the B-25B marked a significant evolution in the Mitchell bomber’s design, particularly in terms of defensive armament and operational readiness.
Design and Features:
- Designation: B-25B (NA-62B)
- U.S. Navy/Marine Designation: PBJ-1B
- British Designation: Mitchell I
- Production: 120 B-25Bs were originally planned, but only 119 were delivered as one aircraft (serial number 40-2243) crashed before delivery.
- First Delivery: August 1941
- Last Delivery: January 1942
Structural and Armament Enhancements:
Defensive Armament: The B-25B introduced powered turrets for improved defense. These included:
- A top turret located in the radio compartment with two .50-caliber machine guns. This turret, designed by Bendix, featured a clear dome and an electric motor for powered operation in both azimuth and elevation. It had a capacity of 400 rounds per gun.
- A lower retractable turret also equipped with two .50-caliber machine guns, with 350 rounds per gun. However, this turret had significant operational issues, including difficulties with target acquisition through the periscope, susceptibility to dirt and damage, and the potential for jamming, which led to its removal in later variants.
Deletion of Waist and Tail Guns: The B-25B eliminated the waist and tail gun positions that were present in earlier models. The large, two-piece waist windows were replaced with smaller, single windows. This deletion was later recognized as a mistake, and these positions were reinstated in later variants (B-25H and B-25J).
Exhaust Modifications: A minor exterior change on the B-25B was the exhaust pipe configuration. The right engine exhaust was modified to a short stub, while the left engine retained the longer pipe due to the presence of a heat exchanger.
Operational History:
- Doolittle Raid: The B-25B gained fame through its use in the Doolittle Raid on April 18, 1942. Sixteen B-25Bs, crewed by personnel from the 17th Bombardment Group, launched from the aircraft carrier USS Hornet to conduct the first air raid on the Japanese mainland.
- Navy and Marine Service: About two dozen B-25Bs were transferred to the U.S. Navy and Marines, where they were redesignated as PBJ-1Bs. These aircraft were used primarily for coastal patrols. By the end of the war, over seven hundred PBJ-1s of various variants were delivered to the Navy.
- Allied Use: The Royal Air Force received twenty-three B-25Bs, designated as Mitchell I, and two were delivered to the Soviet Union. Both the RAF and Soviet Air Force would later receive additional Mitchell bombers.
Performance Specifications:
- Powerplants: Powered by two Wright R-2600-9 engines, each delivering 1,700 horsepower.
- Maximum Speed: 300 mph at 15,000 feet.
- Initial Rate of Climb: 1,704 feet per minute.
- Service Ceiling: 23,500 feet.
- Maximum Range: 1,300 miles with 694 gallons of fuel and a 3,000-pound bomb load, though range varied based on fuel and payload.
- Empty Weight: 20,000 pounds.
- Maximum Take-off Weight: 28,460 pounds.