Abstract: Amphibious vehicle 3 has one or more ducts 9 running from a first to a second end of the vehicle; from vent 5 to vent 7, or vice versa. The vehicle prime mover 19, transmission, brakes, and/or electronic controls, may be cooled in the duct. Fan 19 draws or blows air through the duct. The hull may comprise one wall of the or each duct; hull surface coolers may be provided for cooling liquid. The duct(s) may pass through one or more bulkhead(s) 11, 13 of the vehicle. A separate engine cooling system may comprise a radiator 23 and fans 29. The marine drive may be a jet drive; the vehicle road wheels (6, FIGS. 4 and 6) may be retractable above the vehicle water line when the vehicle is in marine mode.