The 377MGT Mini Guppy Turbine, first flew on March 13, 1970, making it the first of the new generation of the Guppys to fly. Aero Spacelines developed the turboprop conversion on the 377MGT first, then later used the same conversion on the more successful Super Guppys.

The 377MGT was the shortest lived of all the Guppys. The 377MGT was involved in an accident at Edwards Air Force Base on May 12, 1970. With the crash of the 377MGT and the shrinking aerospace budgets, Aero Spacelines found itself no customers for the 377MGT.