The purpose of this site is to highlight the major design, engineering and materials science breakthroughs that gave each iconic World War II warbird its unique flight characteristics. We hope you enjoy!!
The B-25 entered USAAF service in February 1941. By 1942, the B-25 had been upgraded to the C-series which included self-sealing fuel tanks, crew armor protection, a plexiglass dome for navigational sightings, de and anti-icing equipment, heavier nose armament and a remotely operated retractable ventral turret manufactured by Bendix to replace the rear tail-gunner’s position. The B-25C series and B-25D series differed only in the location of their manufacture. The C-series was manufactured at Inglewood, California, whereas the D-series was manufactured at Kansas City, Kansas. 3,052 B-25C/Ds were produced.
The primary purpose of this page is to understand the strengths and weaknesses of the B-25C/D-series defensive armament.
Armament: Defensive armament of the B-25C/D series consisted of six Browning Army-Navy M2 0.50 calibre machine guns.
The AN M2 had a maximum fire rate of 600 to 800 rounds per minute, however, this maximum rate of fire was never sustained. Gunners used 5 to 7 round bursts, with pauses between each burst, to maintain acceptable operating temperatures and conserve barrel life.
Ammo belts contained a mix of Armor-Piercing rounds, High-Explosive rounds, Armor-Piercing-Incendiary rounds and Armor-Piercing-Incendiary-Tracer rounds. Gunners typically began engaging enemy aircraft when they approached within 600 yards. Assuming a best-case muzzle velocity of 2,800 feet per second, the 0.50 calibre round would take 0.7 seconds to reach a target at 600 yards, and, the round would have dropped 69 inches during its flight (Shooters Calculator dot com). Over the same time period of 0.7 seconds, a fighter approaching at 320 miles per hour would have moved 327 feet from its original position. Considering that fighters rarely used straight level approaches and that wind speed and air density also needed to be taken into consideration, a moving bomber did not provide an ideal gunnery platform.
The ventral/belly turret: The ventral turret was manufactured by Bendix and housed two 0.50 calibre Browning machine guns. The turret could fully rotate 360 degrees, giving it a complete downward facing field of fire, but it could not elevate its guns past zero degrees upwards. It was electronically operated with variable speed. To reduce air resistance it was retractable using the aircrafts hydraulic system. The gunner did not sit at a remote station, he knelt with his chest facing down on a chest support over top of the turret. A periscopic sight was used for aiming, which severely restricted visibility, and produced a ‘reverse image’. This combination of restricted visibility and moving reverse image induced intense vertigo and nausea in many gunners! The turret proved difficult to use and was considered ineffective. Generally disliked by crews, it was often removed in the field, sometimes being replaced with a window and flexible mounted 0.50 calibre machine gun. The Bendix ventral turret was deleted from production in the middle of the G-series production run.
The dorsal/upper turret: The upper turret was also manufactured by Bendix and housed two 0.50 calibre Browning machine guns. The Bendix 250CE-3 (also known as the A-9A) was electronically operated and was mounted just back of midship. With variable speed, it had 360 degrees of rotation and could elevate its guns up to 82 degrees but it could not depress its guns below Zero degrees downwards. It did not have a manual combat mode. It was aimed using either an N-6A or N-8 optical reflector sight. Armor plating protected the gunner on the front, and rotated with the turret.
Front mounted machine guns: The B-25 C/D had two forward facing 0.50 calibre AN M2 Browning machine guns. One was fixed and the other was mounted in a flexible ball-and-socket mount, aimed by the bombardier using a ring-and-post sight. The fixed gun was fired by the pilot using an N-3B optical sight mounted on the upper left of the instrument panel.
Defensive Strengths: Aircraft making level attacks from the back or sides may be targeted by both upper and lower turrets whilst the attacking plane is far enough away. Aircraft making level attacks from the front were targeted by the front fixed and flexible guns. The intercom was used to communicate the direction of incoming attacks so that other gun stations could defend against an approach and so that they could also target the bandit while it was disengaging in the direction opposite to their initial attack.
Defensive weaknesses: Due to restricted vision and difficulty targeting because of the reverse image provided by the periscope sight, the B-25C/D was vulnerable to attacks from below.
In closing: The B-25 Mitchell was a versatile and reliable medium bomber that played a significant role in World War II and beyond. Its adaptability and durability made it a favored aircraft among both aircrews and military strategists, however, its ineffective ventral turret did make it vulnerable to attacks from below.