Upon its introduction during the latter years of the Second World War, the Sea Otter was primarily tasked with maritime patrol and air-sea rescue duties by both the RAF and the Royal Navy.

In February 1936, Mitchell approached the Air Ministry's Director of Technical Development to determine desirable performance attributes in the tentative aircraft prior to the detailed design commencing.

From these discussions, it was decided to pursue a dive bombing capability, an elevated loaded weight, longer range, and for it to be fitted with equipment for operating from both aircraft carriers and cruisers.

The propeller was changed again, this time to a four-bladed unit of which the pairs of blades were unusually set at an angle of 35° instead of the usual 90° so that the aircraft could be more easily moved within shipborne hangars and other enclosed areas.

[3] During February 1939, sea recovery trials were begun from HMS Pegasus, resulting in some deviations being made from the standard practices used for deploying the earlier Walrus.

The British Admiralty requested some changes, including that the nose be reprofiled to reduce its tendency to spray water, as well as the installation of a three-blade Rotol constant speed propeller.

[5] A contract for 190 Sea Otters was issued to Blackburn Aircraft later in 1940, but the contact with the company was cancelled the following year, as it was unable to accommodate the extra workload.

[6] Accordingly, it wasn't until January 1942 that the Air Ministry placed a production order for the Sea Otter with Saunders-Roe, who had previously manufactured the Walrus as well.

As they were intended for use as bush airplanes in remote areas, versatility was an important aspect; to allow cargo to be carried, the cabin floor was strengthened and fitted with lashing points, and the passenger seats made easily removable.

[10] During November 1944, the Sea Otter was introduced to operational service; by the time that the type was inducted by its fourth squadron, the Second World War had ended.

While the aircraft primarily performed naval reconnaissance missions , it proved to be superior to its Walrus predecessor in the secondary role of retrieving aircrews from the sea.

[13] Overseas military airwings were quick to procure the Sea Otter following the end of the war, often purchasing aircraft from the British Government.