Fixed-wing transport aircraft are defined in terms of their range capability as strategic airlift or tactical airlift to reflect the needs of the land forces which they most often support. These roughly correspond to the commercial flight length distinctions:
3 to 6 hours
A more specialised role of a cargo aircraft is that of transporting fuel in support of other aircraft with more limited flight endurance such as fighters or helicopters. Smaller cargo aircraft, known as "utility", are often used to transport military communications equipment as temporary or permanent platforms, and in the command role by providing airborne command post or as an air ambulance.
Military transport helicopters are used in places where the use of conventional aircraft is impossible. For example the military transport helicopter is the primary transport asset of US Marines deploying from LHDs and LHA. The landing possibilities of helicopters are almost unlimited, and where landing is impossible, for example densely packed jungle, the ability of the helicopter to hover allows troops to deploy by abseiling and roping.
Transport helicopters are operated in assault, medium and heavy classes. Air assault helicopters are usually the smallest of the transport types, and designed to move an infantrysquad or section and their equipment. Helicopters in the assault role are generally armed for self-protection both in transit and for suppression of the landing zone. This armament may be in the form of door gunners, or the modification of the helicopter with stub wings and pylons to carry missiles and rocket pods. For example the Sikorsky S-70, fitted with the ESSM (External Stores Support System), and the Hip E variant of the Mil Mi-8 can carry as much disposable armament as some dedicated attack helicopters. The assault helicopter can be thought of as the modern successor to the military glider. Finally, there is the generic term utility helicopter, which generally refers to medium-lift designs.
Not all militaries are able to operate a full range of transport helicopters, so the medium transport type is probably the most useful compromise and probably the most common specialist transport type. Medium transport helicopters are generally capable of moving up to a platoon of infantry and are capable of being able to transport towed artillery or light vehicles either internally or as under-slung roles. Unlike the assault helicopter they are usually not expected to land directly in a contested landing zone, but are used to reinforce and resupply landing zones taken by the initial assault wave. Examples include the unarmed versions of the Mil Mi-8, Super Puma, and CH-46 Sea Knight.