Abstract: In one embodiment, the inlet gearbox includes a gearbox housing which is removably coupled to a fan module. The gearbox includes a horizontal gear for removably mating with gear teeth on the stub shaft of the compressor module. The gearbox includes vertical gear means coupled to the horizontal gear means for developing a drive output of the gearbox. A single main shaft bearing is fixedly disposed in the gearbox housing. The main shaft bearing supportably receives a rearward extension of the horizontal gear. The stub shaft is inserted into the rearward extension of the horizontal gear. The main shaft bearing provides the sole rotational support for the horizontal gear of the modular inlet gearbox and for the forward end of the stub shaft of the compressor module. The main shaft bearing is disposed in the inlet gearbox housing in a controlled environment prior to assembly of the inlet gearbox into the gas turbine engine.