 The EX-2A was to have its counter-rotating propeller driven directly by an electric motor, while the EX-2B was to use a gas turbine connected to a gearbox.After an accident with the proposed fuel for the EX-2B (Propyl Nitrate) the US Navy ordered the halting of its use.This resulted in the EX-2B development team shifting to an electric motor using the design for a jet engine starter motor as the basis to give the high torque and RPM the counter-rotating gearbox needed.