CHINA LAKE NATIC (40mmHE).

This was a modernization of the M79 grenade launcher, developed in the China Lake US Navy Range; a pump-action, 4-rounds capacity device, developed as an experimental support weapon for he Navy SEALS (actually, a modified M79, an attempt to cheaply update the M79 GLs still in use by the US armed forces, in order to avoid the massive expense to replace the M79 with the XM148 and M203 UBGLs). It never entered in production, however.

Picture from Giovanni Tendas