The HMS Dasher (D37) was a British Royal Navy (RN) shortest-lived aircraft carrier of the Avenger class. It was a small and slow type aircraft carrier used by the RN, the US Navy, the Imperial Japanese Navy and Imperial Japanese Army Air Force in World War II. The Avenger-class escort carrier was comprising three ships in service during the Second World War. All were originally the American type 3 merchant ships. The name Riode Janeiro was laid down on 11 March 1940, launched on 12 April 1941 and finally commissioned into RN service as HMS Dasher D37 on 2 July 1942. The Dasher sailed to the River Clyde on March 1943 and escorted one convoy successfully. But shortly after leaving with the second the Dasher suffered engine trouble and returned. Afterwards, getting to the mouth of the River Clyde (The Firth of Clyde) on 27 March 1943, the Dasher suffered a major internal explosion and sank.

The Lend-Lease policy, formally titled an Act to Promote the Defence of the US, enacted March 11 1941, was a program under which the HMS Dasher (D37) transferred to RN in 1942. The President Roosevelt's top foreign policy adviser Harry Hopkins had effective control over Lend lease. The Dasher-D37 had a complement of 555 men and an overall length of 42 ft 3 in (150.04 m). It displaced 8,200 long tons at deep load. The death of D37 was 379 out of 528 crew men.

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