The Bristol Blenheim Mk IV had originally been developed as the Bristol Bolingbroke. While that name was abandoned for British production, it was revived in 1937 to distinguish aircraft produced under license in Canada by Fairchild Aircraft.
The Bolingbroke was only used by the R.C.A.F. It was first issued to No. 8 (Bomber Reconnaissance) Squadron late in 1939, and used for coastal reconnaissance.
The Bolingbroke’s war did not really start until 1942. In that year two squadrons were sent to Alaska and the Aleutian Islands (No. 115 arriving in April, No. 8 in June). There the Bolingbroke engaged in anti-submarine patrols, gaining a share in the sinking of the Japanese submarine Ro32 on 7 July 1942 (shared with the U.S. Navy).
The majority of Bolingbrokes were used in the Commonwealth Air Training Plan, which allowed R.A.F. pilots to train in safety in Canada.
The first 18 Bolingbrokes were identical to the Blenheim Mk IV, including British instrumentation.
The eighteen Mk Is were also used to test out new designs. One aircraft was rebuilt after a crash to use American instruments, and redesignated the Mk II. Experience from this model would be used on the Mk IV.
Two more Mk Is were converted into float planes during 1940, using two Edo floats. The use of float planes was investigated by most sides in the Pacific war where the long distances involved and lack of suitable airfields made sea planes seem desirable. In most cases, the addition of the floats reduced the performance of the aircraft to unacceptably low levels. The Bolingbroke Mk III did not enter production, and the two prototypes were converted back to Mk Is during 1942.
The Bolingbroke Mk IV was the standard version of the aircraft. It used the 905 hp Mercury IV engine (late production used the Mercury XX, with 950 hp) and American instrumentation. 151 Mk IVs and 457 Mk IV-Ts were produced in total.
Fourteen of the 151 Mk IVs were build using the Pratt and Whitney Wasp Junior engine (825 hp). The type was developed to guard against any shortage of Mercury engines, but not shortage developed.
Another engine tried out in the Bolingbroke was the 900hp Wright-Cyclone GR-1820-G3B. Tests revealed that this engine did not produce a significant improvement in performance, so the type did not enter production.
The most numerous version of the Bolingbroke was the Mk IV-T, used as a trainer. In total 457 Mk IV-Ts were built, with the first deliveries in March 1942. The final 57 were powered by the Mercury XX-star engine. Another 51 airframes were completed, but not delivered.
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