When the aircraft carrier was proven a viable sea-going warship in World War 1 (1914-1918), military powers who could afford such ships moved on developing dedicated naval aircraft like fighters and reconnaissance types. Avro (A.V. Roe), an aviation company known primarily for its Royal Air Force (RAF) contributions, sold a rare naval aircraft product to the Royal Navy as the "Bison". This ugly aircraft held a short service life from 1922 to 1929 and saw initial use under the Royal Air Force (RAF) banner. The aircraft - along with the competing Blackburn R-1 (44 examples) - were used to fulfill Specification 3/21 calling for a "naval fleet spotter/reconnaissance aircraft". The Avro design took on the model name of "Type 555".
Both Avro and Blackburn were commissioned to provide three. The Avro design became an awkward-looking creature retaining the typical biplane wing configuration common to many 1920s aircraft. The wings included an upper and lower wing plane with dihedral (upward angle) seen on the upper wing span. The engine was mounted at front in typical fashion with a fixed, wheeled undercarriage set under the aircraft (a tail skid was used under the tail). The pilot's position was of note, seated immediately aft of the engine installation yet ahead of the upper wing section for a commanding view of the action ahead from his open-air placement (just a forward windscreen was featured). The fuselage was given a very deep look which allowed for the occupants within to stand. This cabin crew numbered three and included a navigator, radioman, and machine gunner. Each side of the fuselage featured a large rectangular-shaped window for observation and the machine gunner manned his post along the dorsal spine of the aircraft, just above the cabin area. His weapon - a single .303 Lewis machine gun - was mounted to a Scarff ring which allowed for trainable fire against any approaching enemy aircraft. The tail unit of the aircraft was largely conventional save for the vertical fin which was given a rather oblong, strange shape.
Power for the Bison was through a Napier "Lion II" series engine developing 480 horsepower while driving a two-blade propeller. Maximum speed was 108 miles per hour with cruising speeds near 90 miles per hour. Operational range was out to 360 miles with a service ceiling reaching 12,000 feet and a rate-of-climb of 450 feet per minute.
Beyond the sole .303 machine gun, the aircraft was given provision to carry bombs under the wings.
The Type 555 prototype first flew in 1921 and was quick to showcase handling issues related to its unconventional looks. The dihedral design feature of the upper wing element was removed and its center area raised by two full feet to compensate. Three Type 555 prototypes were completed while twelve production examples were ordered under the "Bison" name. Despite their intended use by the Royal Navy, first examples were actually operated by the RAF in 1922. The FAA would ultimately field the Bison across squadrons 421, 423, 447, and 448 and these served into 1929 before being succeeded themselves by the Fairey IIIF biplane.
A few variants dotted the short history of the Bison: The Bison I designation was used to signify the original batch of twelve aircraft and Bison IA followed as rebuilt Bison I aircraft with a gap introduced in the biplane arrangement and changes to the tail. Bison II (Type 555A) was an improved form with modified wings and twenty-three of this type were built. Bison I (Type 555B) became a "one-off" example modified as a prototype amphibious aircraft but not adopted for service.
A total of 55 Bison aircraft were realized. Due to their particular appearance during the 1920s, the type never recorded any combat action during its service tenure aloft. It was also never exported.
Status Retired, Out-of-Service
[ 55 Units ] : Avro - UK
- Ground Attack
- Navy / Maritime
- Reconnaissance (RECCE)
36.02 ft (10.98 m)
46.00 ft (14.02 m)
14.17 ft (4.32 m)
(Showcased structural dimension values pertain to the Avro Bison II production model)
4,123 lb (1,870 kg)
6,140 lb (2,785 kg)
(Showcased weight values pertain to the Avro Bison II production model)
1 x Napier Lion II engine developing 480 horsepower.
(Showcased powerplant information pertains to the Avro Bison II production model)
109 mph (175 kph; 94 kts)
12,008 feet (3,660 m; 2.27 miles)
360 miles (580 km; 313 nm)
450 ft/min (137 m/min)
(Showcased performance values pertain to the Avro Bison II production model; Compare this aircraft entry against any other in our database)
1 x .303 Vickers machine gun in fixed, forward-firing position.
1 x .303 Lewis machine gun on trainable ring mounting
Conventional drop bombs carried under the wings.
(Showcased armament details pertain to the Avro Bison II production model)
Avro Bison - Base Series Designation
Avro 555 Bison - Prototypes; three examples
Avro 555 Bison I - Fitted with Lion II engine; twelve examples; later revised to Bison IA standard.
Avro 555 Bison IA - Dorsal fin added; biplane gap wings
Avro 555A Bison II - Improved variant; 23 examples
Avro 555B Bison I - Amphibian conversion model; single example not adopted for service.
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