Construction of the fighter prototype, W4052 was also carried out at the secret Salisbury Hall facility.

Yak-50 (1949 - fighter prototype, development of Yak-30, designation reused)

The Fairey F.2 was a British fighter prototype in the late 1910s.

The Grigorovich I-1 was a Soviet fighter prototype of the 1920s.

The Bristol Type 101, was a British two-seat fighter prototype in the 1920s.

The Heinrich Pursuit was an American fighter prototype of the 1910s.

There was also another aircraft named Yak-25 - a light fighter prototype of 1947.

Two more fighter prototypes were built as SAI.207s, flying for the first time in the Spring of 1941 and 1942.

The Pomilio Gamma was an Italian fighter prototype of 1918.

The gain mainly reflects the absence of costs for developing and testing advanced tactical fighter prototypes, which have been completed.