The Blackburn B-5 Baffin was a biplane torpedo bomber designed and produced by the British aircraft manufacturer Blackburn Aircraft. It was a development of the Ripon, the chief change being that a 545 hp (406 kW) Bristol Pegasus I.MS radial engine had replaced the Ripon's Napier Lion water-cooled inline engine.

The Baffin was designed by Major F. A. Bumpus and was initially pursued as a private venture. It was a conventional two-seat single-bay biplane of mixed metal and wooden construction with fabric covering. It had swept, staggered, equal-span wings, the lower having an inverse gull to provide clearance for the torpedo while retaining a short undercarriage. The engine was shifted forwards in comparison to that of the Ripon to retain its centre of gravity. Armament comprised a fixed forward-firing 0.303 in (7.7 mm) Vickers machine gun and one free-mounted 0.303 in (7.7 mm) Lewis gun in the rear cockpit, plus one 2,000 lb (910 kg) bomb, or 1,576 lb (715 kg) Mk VIII or Mk IX torpedo, or three 530 lb (240 kg) or six 250 lb (110 kg) bombs.

First flown on 30 September 1932, the project caught the interest of the Air Ministry, who produced Specification 4/33 around the aircraft and placed an initial order with Blackburn for it in early 1933. The Baffin was initially procured for the Fleet Air Arm (FAA), who transferred many of their Ripons to Blackburn for remanufacturing into the Baffin configuration; new-build aircraft were also produced. During January 1934, it was introduced to service. It had a relatively short service life with the FAA, who elected to withdraw the type in favour of newer aircraft prior to the outbreak of the Second World War in September 1939. The only export customer for the Baffin was the Royal New Zealand Air Force, who had acquired 29 existing aircraft from Britain during 1937. These were largely used in reserve roles and for training, and were only operated for a short period into the conflict until their withdrawal sometime in 1941.

During the early 1930s, the torpedo bomber squadrons of the FAA were equipped with the Blackburn Ripon. While the Ripon had only entered service in 1930, it was powered by the elderly Napier Lion engine. As early as 1928, Blackburn had recognised that the replacement of the Lion with a modern air-cooled radial engine would present several advantages. Dispensing of the Lion's heavy water-cooled radiators would reduce weight and thus increase payload; air-cooling would also simplify maintenance. The company had initially pursued this direct when it dought export sales, an alternative powerplant in the form of the Armstrong Siddeley Tiger engine was adopted on those Ripons sold to Finland.

Blackburn remained keen to use low-weight radial engines for its fighters during the early 1930s. It drew up plans for a reengining of existing Ripons with either the Armstrong Siddeley Tiger and the second by the Bristol Pegasus engines, which were viewed as having particularly promising performance. As the detailed design of the aircraft was produced, there were no meaningful changes to the airframe save for a new type of engine mounting that was projected on steel struts and was also shifted forwards so that the aircraft's centre of gravity could be maintained.

During 1932, Blackburn decided to build two prototypes of radial-engined Ripons, each powered by one of these engines, as a private venture (i.e. without an order from the Air Ministry). Both of the prototypes were completed in September 1932. On 30 September 1932, the Pegasus-engined prototype conducted its maiden flight, flown by A. M. Blake. Following the completion of manufacturer tests, in February 1933, the two prototypes were delivered to RAF Martlesham Heath, Suffolk, for competitive evaluation flights. Partway through the evaluation, the aircraft were briefly returned to Blackburn at Brough to be fitted with bomb rails and a Townend ring. The Air Ministry paid attention to these trials and expressed its preference for the Pegasus-powered version of the aircraft.

During early 1933, Specification 4/33 was written around the aircraft for it to serve as a short-term replacement for the FAA's Ripons. An initial order was issued to Blackburn for a pair of pre-production aircraft, which were speedily constructed. In April, acceptance trials at Martlesham Heath had commenced with the first pre-production aircraft, while the second remained at Brought for trial installations. Sea trials were later performed aboard the aircraft carrier HMS Courageous; on 2 February 1934, the first catapult-assisted takeoff was performed at RAE Farnborough. During September 1933, it was announced that the Air Ministry had approved the name Baffin.

On 10 November 1933, the first production aircraft made its first flight. Work was underway on the production of 26 new aircraft along with 38 conversions of airframes from Ripons; the airframes were extensively refurbished. The aviation author Aubrey Joseph Jackson noted that the rate of manufacturing was particularly fast. During 1935, a further 26 conversions of Ripons into Baffins were ordered due to the reliability problems that had become associated with the Armstrong Siddeley Tiger engines that had powered the Blackburn Shark. A further factor was the political desire to expand the strength of the Fleet Air Arm. An additional three new production Baffins had the 580 hp (430 kW) Pegasus II.M3 engine and were termed the Baffin T8A. The aircraft is said to have inspired the coining of the word "Boffin".^{[citation needed]}