Blackburn Cubaroo


The Blackburn T.4 Cubaroo was a prototype British biplane torpedo bomber of the 1920s. Built by Blackburn Aircraft and intended to carry a large 21 in torpedo, the Cubaroo was one of the largest single-engined aircraft in the world at the time of its first flight.

Design and development

In 1921, the British Air Ministry issued Specification 8/21 to Blackburn for a Coastal Defence Torpedo Aeroplane, the resulting design being the T.4 Cubaroo. Due to the change of policy in the Air Ministry to favour a twin-engined design a new specification was issued in 1922, the British Air Ministry drew up Specification 16/22, for a long-range torpedo bomber capable of carrying a 21 in torpedo over a range of. Major F. A Bumpus, chief designer of Blackburn Aircraft submitted the design for the Blackburn T.4 Cubaroo, which was a large biplane powered by a single example of the new 1,000 hp Napier Cub engine. Avro also submitted a design against this specification, the Avro 557 Ava, which was a similarly large biplane, powered by two 600 hp Rolls-Royce Condor engines.
To carry the heavy torpedo over a long range, the Cubaroo was massive. With a wingspan of, it may have been the largest single-engine military aircraft in the world at the time and was fitted with the most powerful aircraft engine available, the Napier Cub, which was an unusual X-type engine which weighed over a ton excluding radiators. The Cubaroo, with a mainly metal structure, had a deep fuselage to accommodate the Cub engine and was fitted with folding, two-bay wings. To carry the torpedo, the Cubaroo was fitted with a main undercarriage comprising two sets of two wheels, with the torpedo being carried on a crutch between them.

Operational history

The first prototype flew in secrecy in the summer of 1924, proving to have good handling characteristics, with the engine not causing problems. It was then fitted with a metal, three-blade adjustable-pitch propeller and was delivered for testing at RAF Martlesham Heath but was written off after its undercarriage collapsed on 2 February 1925. A second prototype flew in 1925, but the Air Ministry abandoned the requirement for a torpedo bomber to carry the 21 in torpedo and lost interest in single-engine heavy bombers, so the second prototype Cubaroo was used as an engine testbed, flying with the experimental 1,100 hp Beardmore Simoon compression ignition engine.

Operators