 There was considerable development of the power plant/propeller combination during the design of the Sea Otter, which at its conception was called the "Stingray".The original test aircraft had a Bristol Perseus XI radial engine with a two-bladed propeller, which gave insufficient thrust so a two-position three-blade propeller was substituted, later changed again to a four-bladed type with the pairs of blades set at an angle of 35°, instead of the usual 90°.The first flight took place on 23 September 1938, but it was not until January 1942 that the Air Ministry placed a production order.