In 1964, Prince entered their new S54 Skyline GTs in the second Japanese Grand Prix, hoping to prove the performance potential of the car's new G-7 straight-6.

Although the cars performed well, they were defeated by a privately entered Porsche 904, leaving the Skylines to take second through sixth positions.

Realizing the superiority of the mid-engine design used on the Porsche 904, Prince decided that a custom-built sports car would be needed to win the Japanese Grand Prix.

The rear buttresses were replaced with a flowing cockpit and engine cover, while the vents and ductwork of the car was further refined.

Due to the cancellation of the Japanese Grand Prix in 1965, the R380 was used by Prince to test high speed aerodynamics.