An amphibious vehicle is any type of transport that can be driven or otherwise operated both on land and in water. The size and function of the amphibious vehicle can vary significantly, and it will be classified as such as long as it can be operated in a feasible manner both on land and on water. Vehicles that detach from one part during the transition between land and water are generally not considered to be amphibious, nor are airplanes that land and take off from water.
Some models of amphibious vehicle travel both on land and water by using an inflatable skirt that creates a cushion of air to propel the craft. These models are generally known as hovercrafts. Other models of amphibious vehicle use propulsion devices such as tires or tracks on land and water propulsion devices in water. The undercarriage and engine of the crafts will need to be sealed off to prevent water from damaging the engine, as well as to provide buoyancy; the undercarriage often acts as a hull when floating in the water. The original intent of these vehicles was to enhance off-road capabilities of military vehicles, allowing them to operate on land, in inclement conditions such as mud or snow, and over water.
Recreational vehicles now often feature amphibious capabilities as well, and some models are even designed for racing. Hovercraft have been designed to be small, light, and fast, making them popular among recreational racers. They are also commonly used for search and rescue operations, passenger transport, and military transport. Hovercraft are expensive to build and maintain, and while they tend to be faster than other transport options and can make the transition between land and water at high speeds, they are not used as often as other types of transport for military purposes because they can expensive to operate as well as very loud during operation.
Many tanks and armored vehicles are designed to be amphibious. An amphibious vehicle designed as a tank will often feature treads rather than tires for durability and mobility over rough terrain, and the body of the tank will be bulletproof or damage-resistant. The bottom of the tank will be enclosed like a hull as well for buoyancy and ease of steering while submerged in water. Some tanks feature detachable pontoons that act as flotation devices for the tank, since many tanks are too heavy to be buoyant on their own.