Gryphon (Great Britain, Tier-10, HT, promotional, mechanics: 2-round magazine with reverse reloading)
Historical Reference:
As work on the Chieftain tank progressed, the matter arose of organizing production of a similar-class vehicle outside of the U.K. Based on the chassis of the first prototype, a project was developed with the American turret of the promising Concept1b tank.
The vehicle was given the working name of Gryphon. Besides the turret, use of a range of other American components was planned. The internal equipment was meant to remain British. Initially, the design included the possibility of mounting either a British or an American gun, depending on the country where production was supposed to begin. The project was closed in favor of more promising vehicle types. 
