B-25H of the 12th Bomb Group over Italy 5

Operational experience with the B-25G demonstrated that the concept of a heavily armed flying artillery platform was indeed valid. The 75-mm cannon proved effective against a variety of targets, particularly coastal shipping and even warships up to the size of a destroyer. However, the B-25G also had significant limitations, which led to the development of the B-25H to address these shortcomings.

One of the major deficiencies of the B-25G was its lack of defensive armament, especially after the lower turret was removed during production. Although the addition of tail and waist gun positions at depots provided some improvement, these modifications were not a comprehensive solution. A significant issue was that the top turret was located in the aft fuselage compartment, which restricted the effective use of any added waist guns in the cramped space.

To resolve this, in the B-25H, the top turret was relocated forward to the navigator’s compartment, just behind the cockpit. This change necessitated moving the ADF “football” antenna to the underside of the forward fuselage and eliminating the astrodome and side scanning windows in the navigator’s compartment. Two small armor fairings were added to the top of the fuselage, just aft of the gun muzzles, to deflect bullets away from the tail gunner’s position in case the top turret guns were accidentally fired while in the stowed position pointing aft.

By moving the turret forward, the rear fuselage compartment was opened up for more effective use of the waist guns. Staggered waist gun positions were added, which were slightly bulged and covered with perspex. Each position housed a .50-caliber machine gun, mounted through an opening in the lower aft corner of each window, sealed by a canvas boot around the barrel. The radio operator, who also managed the cameras in the aft fuselage, manned both guns depending on the combat situation. With the top turret out of the way, he had greater freedom of movement. The ammunition for these guns was fed through chutes from overhead storage boxes, each containing 200 rounds.

Contrary to what has been reported in some publications, the navigator/cannoneer in the B-25H was not the radio operator, although some radio equipment was relocated to the area where the co-pilot’s rudder pedals were located on other versions. The majority of the radio gear, along with the radio operator, remained in the aft fuselage compartment.

A significant improvement with the B-25H was the introduction of a proper and effective tail turret. To accommodate this, the depth of the aft fuselage was increased by seven inches. The Bell electro-hydraulic turret was equipped with two .50-caliber machine guns, each supplied with 600 rounds of ammunition. The gunner operated the turret while seated on a stool under a framed greenhouse, similar to the depot-installed turrets on some B-25Cs, Ds, and Gs, but slightly wider and deeper.

With the addition of the tail and waist gun positions, the defensive armament of the Mitchell was significantly improved. Additionally, during attacks on surface targets, the top turret gunner could aim his weapons forward to augment the nose-mounted guns’ firepower.

The number of .50-caliber machine guns mounted in the nose was increased to four, compared to just two in the B-25G. The first 300 B-25H-1-NAs featured two single gun packs on the right side of the forward fuselage, with no packs on the left. Later production blocks added two guns on both sides, allowing a B-25H from these blocks to bring ten .50-caliber machine guns and the 75-mm cannon to bear on its target when the top turret guns were aimed forward. The cannon installed in the B-25H was the T13E1 version, which was lighter than the M4 used in the B-25G, though it still required manual loading and could only fire one round at a time. In some cases, the cannon was removed in the field and replaced with two .50-caliber machine guns when these were more suitable for the mission.

The co-pilot’s station was eliminated, and the seat was repurposed for the navigator/cannoneer. The co-pilot’s yoke and rudder pedals were removed, and the instrument panel was redesigned for use by a single pilot. Bomb release controls were relocated to the cockpit for the pilot’s use since there was no bombardier. An A-1 pilot bomb sight was mounted on an N2B gun sight for minimum altitude bombing, with a ring and bead sight as a backup. A fold-down chart board was also provided for the navigator/cannoneer.

The B-25H was also the first Mitchell variant to include pilot armor plating as a production standard. Externally, the carburetor air intakes above the engine nacelles were enlarged, and the shrouds on the two right oil cooler vents were removed. A circular emergency escape hatch was added on the right side of the aft fuselage. Electric bomb controls and a gun sight aiming camera were added starting with B-25H-5-NA production. However, the ability to carry a 2,000-pound bomb was deleted beginning with B-25H-5-NA, serial number 43-4535.

The XB-25H prototype was converted from B-25C-10-NA, serial number 42-32372, and was followed by 1,000 production aircraft. These were divided into three production blocks: 300 B-25H-1-NAs, 300 B-25H-5-NAs, and 400 B-25H-10-NAs. The last B-25H-10-NA to be produced was also the final Mitchell built at Inglewood, California. This aircraft, named “OLD BONES,” was signed by the workers who built it and later served with the 81st Bomb Squadron of the 12th Bomb Group, still bearing the signatures on its natural metal skin. Subsequent production of the Mitchell continued with the B-25J variant, produced in Kansas City, Missouri.

The U.S. Navy acquired 236 B-25Hs, redesignating them as PBJ-1H. These aircraft were extensively used by Marine squadrons in the Pacific in the anti-shipping role. Others flew sea patrol missions along the U.S. coastline, and one was even used for carrier suitability experiments aboard the USS SHANGRI-LA, CV-38.

Data:

Version: B-25H
North American Model Number: NA-98
U.S. Navy/Marine Designation: PBJ-1H
British Designation: None
Number Built: 1,000
First Flight: May 15, 1943
First Delivery: August 1943
Last Delivery: July 1944
Powerplant: Wright R-2600-13
Maximum Horsepower (each): 1,700
Maximum Speed: 275 mph at 13,000 feet
Initial Rate of Climb: 790 feet per minute
Ceiling: 24,800 feet
Ferry Range: 2,700 miles
Empty Weight: 19,975 pounds
Maximum Take-off Weight: 33,500 pounds