A power train for an amphibian includes a first prime mover, a first land propulsion unit, and a first marine propulsion unit. The first prime mover is arranged to selectively drive the first land propulsion unit, or the first marine propulsion unit, or both. The power train further comprises a second prime mover. The second prime mover is arranged to selectively drive the first land propulsion unit, or the first marine propulsion unit, or both, either in place of the first prime mover or in addition thereto.