Fred Slingsby designed the Type 12 Gull to be relatively inexpensive and easy to fly in the hands of the inexperienced pilots in the UK.

Slingsby had had a bad experience with the Type 9 King Kite entering incipient spins at low airspeed which was ascribed to the use of a NACA 4312 aerofoil section at the wing-tips, so he designed the Gull with a modified RAF 34 profile at the tips.

The cause of the wing drop problem on the King Kite was later found to be inaccurate manufacture, but the Gull retained the modified RAF 34 section.

With the tight post-war economy within Britain, gliders of simplified production quickly became a factor in being able to produce cost-effective sailplanes.

[citation needed] It went on to have a long and distinguished career, and was owned at one point by Prince Bira of Siam, who was at the time the World Motor Racing Champion.

Bira had bought the Gull III in 1944 and flew it in the company of his dog, a small white West Highland Terrier called "Titch", on many epic flights, including one to 12000 ft.

Its C of A expired again in July 1974 because its wing had been damaged by damp (casein glue failure) during the previous winter, when it had been left out in its closed trailer at St. Mary's Farm, Clifton, near Deddington, Oxon.