The purpose of the main reduction gear in a marine gas turbine propulsion installation is which of the following?

Correct Answer: Option A — Transfer high-speed gas turbine rotation to low-speed propeller rotation.

Marine gas turbines operate at extremely high rotational speeds, which are incompatible with efficient propeller operation. The main reduction gear is essential to step down these high turbine speeds to the lower, efficient rotational speeds required for the propeller, enabling effective thrust generation for vessel propulsion.