A Grizzly with a gun

by Dr. Marshall Michel
52nd Fighter Wing historian

One of the most successful aircraft types for the U.S. Army Air Forces and Royal Air Force in World War II was the fast, very heavily armed twin engine ground attack aircraft used for low level attack missions, notably the Bristol Beaufighter, the de Havilland Mosquito and the North American B-25 Mitchell.

Some models of both the Mosquito and the B-25 were fitted with a single heavy cannon to provide extra hitting power and accuracy during their attack. The “Tste” Mosquito successfully carried a 57 millimeter standard Army light artillery piece modified with a Molins automatic loader that fired one round a second. The B-25, on the other hand, carried a much heavier 75 millimeter cannon whose 14-pound shell had to be loaded by hand, giving a rate of fire of one round every five seconds, and was considered less successful.

Still, it was obvious that the airborne 75 millimeter cannon would be a formidable weapon. In early 1942, Beech aircraft, well known for its civilian light twin engine transports, had proposed a bomber destroyer — the Beechcraft Model 28 — armed with a 75 millimeter cannon to the U.S. Army Air Force.

A bomber destroyer was seen as unnecessary, but in December 1942 the service awarded Beech a contract to modify the Model 28 into a ground attack aircraft to attack tanks, bunkers, and shipping. Beech was told to build two prototypes under the designation XA-38, which was dubbed the “Grizzly” soon after construction began.

The Grizzly was built around a nose-mounted, fully automatic T15E 75 millimeter cannon with 20 rounds and a  rate of fire of one of the 14-pound rounds a second. The cannon barrel protruded from the nose cone assembly, giving the Grizzly a swordfish appearance.

The entire forward section of the nose was arranged on counterbalanced springs to open like the hood of an automobile and expose the 75 millimeter cannon for ease of servicing and reloading. The nose section, complete with cannon, could be removed and replaced with other nose sections equipped with other armament arrangements.

The pilot also had two fixed .50 caliber Browning machine guns under the nose, and defensive armament consisted of four .50 caliber machine guns, two each in remote-controlled ventral and dorsal turrets. They were aimed via periscope sights and fired by the gunner in his rear cabin in a dorsal position near the tail. There were heavy internal armor plates to protect pilot and gunner.

Aside from the cannon nose, structure was conventional and much like the Beech transports.

The fuselage was four main sections for ease of maintenance and repairs. The cannon took up the nose and made tricycle landing gear impossible, so the undercarriage was a typical “tail dragger” with two forward single-wheeled landing gears and a single tail wheel.

The empennage was conventional with a horizontal tailplane with two vertical tails. The forward part of the fuselage in front of the cockpit had a steep slope and gave the pilot the excellent view downward and forward necessary for strafing.

The XA-38 was the size of a medium bomber — a design gross weight of 29,900 pounds, 52 feet long with a 67 foot wing span. Every means possible was employed to decrease drag, including flush riveting of all exposed skin surfaces. On the wings, the slotted flaps had a control system designed to prevent retracting the flaps so fast they would cause the airplane a dangerous sink rate.

To the give the Grizzly the high speed required for low level attack it was fitted with two Wright R-3350-53 air-cooled radial piston engines of 2,700 horsepower, the same engine that powered the B-29, each driving three-bladed, constant speed Hamilton Standard propellers. Cooling of the huge engines — a major problem on the B-29 — was provided by NACA type circular cowlings with careful design of the cowls’ entrance and exit, and cooling was controlled by automatic cowl flaps operated by a control unit having a temperature element in the hottest engine cylinder.

 On May 7, 1944, a Beech test pilot flew the XA-38 on its maiden flight from the company’s Wichita airfield. The aircraft proved satisfactory in all respects and better than expected in some, including top speed. After its first flight, the airplane was flown to Eglin Field, Florida, for performance tests conducted by the Army Air Corps through 1944 and 1945.

The XA-38 had excellent, stable flight characteristics but was most notable for her top speed of 375 mph at low altitude — comparable to the top-flight single-engine fighters of her day.

The XA-38 could also take-off and land in shorter distances than most single-engined fighters and her power plants and airframe proved reliable in subsequent evaluations.

Most importantly, the gunnery tests proved the effectiveness of the heavy armament, and the weapons’ serviceability was also excellent.

However, by this time it was 1945, and it was obvious that the war coming to an end, and in addition to this, the engines for the Grizzly were the same as those used in B-29, which had priority. The few engines that were not slated for that bomber were given to new Navy aircraft programs.

The Grizzly was Beech’s last attempt at a combat aircraft and was another “too late” system that remains a minor footnote in U.S. aviation history, though it had the potential to being one of the war’s top ground attack aircraft.

(For questions or comments, contact Dr. Michel at marshall.michel@spangdahlem.af.mil.)