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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 (533 mm) torpedo, the Cubaroo was one of the largest single-engined aircraft in the world at the time of its first flight.

T.4 Cubaroo
Role Torpedo Bomber
Manufacturer Blackburn Aircraft
Designer F A Bumpus
First flight 1924
Status Prototype
Primary user Royal Air Force
Number built 2


Design and developmentEdit

In 1921, the British Air Ministry issued Specification 8/21 to Blackburn for a Coastal Defence Torpedo Aeroplane, the resulting design being designated 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 (533 mm) torpedo (which was at the time thought capable of sinking the largest warship) over a range of 800 mi (1,300 km).[1] 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 (750 kW) 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 (450 kW) Rolls-Royce Condor engines.

In order to carry the heavy (over 2,000 lb/907 kg) torpedo over a long range, the Cubaroo was massive. With a wingspan of 88 ft (27 m), it may have been the largest single-engine military aircraft in the world at the time,[1] and was fitted with the most powerful aircraft engine available,[2] 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. In order to allow the torpedo to be carried, the Cubaroo was fitted with a main undercarriage comprising two sets of two wheels, with the torpedo being carried on a crutch between the two sets of wheels.

Operational historyEdit

The first prototype (with serial N166) flew in secrecy in the summer of 1924,[1] proving to have good handling characteristics, with the engine not causing problems (the Cub had already been test flown in an Avro Aldershot testbed).[1] 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 (533 mm) 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 (820 kW) Beardmore Simoon compression ignition engine.[1]


  United Kingdom

Specifications (Cubaroo)Edit

Data from The British Bomber since 1914 [1]

General characteristics



  • 3 × .303 in (7.7 mm) Lewis Guns in midship gunners cockpit and at beam hatches
  • 1 × 21 in (533 mm) naval torpedo


  • 4 × 551 lb (250 kg) bombs

See alsoEdit

Aircraft of comparable role, configuration and era


  1. ^ a b c d e f Mason, Francis K (1994). The British Bomber since 1914. London: Putnam Aeronautical Books. ISBN 0-85177-861-5.
  2. ^ Lewis, Peter (1980). The British Bomber since 1914 (Third ed.). London: Putnam. ISBN 0-370-30265-6.
  3. ^ Flight 1959

External linksEdit