In which type of gear drive do the individual propulsion units consist of the main turbines and the main reduction gear?

The correct answer is steam turbine. In a steam turbine gear drive system, the individual propulsion units are comprised of the primary turbines, which generate power by converting steam energy into rotational mechanical energy, along with the main reduction gear. The main reduction gear's function is to adjust the rotational speed of the turbine output to a level more suitable for driving the propulsion system effectively.

This design is common in marine applications where steam is used for propulsion. The integration of the main turbines with the main reduction gear is essential for achieving the desired balance between power output and shaft speed, enabling efficient propulsion.

In contrast, gas turbine propulsion systems also use turbines but are characterized by different operational principles and configurations. Diesel engine drives rely on internal combustion engines and do not typically involve the steam generation process. Electric drive systems utilize electric motors instead of turbines, further distinguishing them from steam turbine designs.