US military's workhorse helicopters

Helicopters are often used to deploy special forces

Helicopters are the workhorses of most modern armies, and the US has developed several highly specialised varieties fulfilling a number of roles.

For movement of troops, heavy equipment and as a medical rescue aircraft, the UH-60 Black Hawk has been the US military's mainstay for nearly 25 years.

It is designed to carry 11 fully-equipped air assault troops, and can move a 105-millimetre howitzer, its crew and 30 rounds of ammunition.

Black Hawks first saw service in 1978

Although highly sophisticated, one of the Black Hawk's great attributes is that it can be easily maintained and repaired in the field.

Modified Black Hawks are also used for command and control, electronic warfare and in special forces operations.

The twin-engined, medium-lift MH60 Pave Hawk is the standard special forces adaptation of the Black Hawk.

Modifications include two removable external fuel tanks, two machine guns and an air-to-air refuelling probe. Two M134 7.62mm 'miniguns' can also be added if needed.

MH-60 Pave Hawk: Special forces mainstay

Pave Hawks are equipped with forward-looking infra-red, a digital map generator, and terrain following radar.

Defensive equipment includes radar and missile warning systems and infra-red jammers.

Flown by the Air Force Special Operations Command, the Pave Hawk's primary roles are infiltration, recovery and re-supply of special forces units operating behind enemy lines, day or night.

The helicopters are fitted with all-weather radar, which enables them to operate in poor conditions.

Pave Hawks saw service during Operation Desert Storm in Iraq in 1991, recovering downed coalition pilots in Iraq, Saudi Arabia, Kuwait and the Persian Gulf.

The MH-53J Pave Low Helicopter is one of the world's largest, and most technologically sophisticated helicopters.

It was developed from the HH-53 Super Jolly Green Giant, which saw service in the Vietnam War in a special operations role.

The Pave Low is the world's most technologically advanced helicopter

The Pave Low fulfils a similar role, performing low-level, long-range missions into enemy territory day or night, in adverse weather, to land, recover or resupply special operations forces.

Carrying 38 soldiers, the helicopter is equipped with terrain following radar, enabling it to fly at a very low level.

The armour-plated Pave Low is usually armed with either three 7.62 mm miniguns or three .50 calibre machine guns.

MH-53J's played an important role in the Gulf War, guiding AH-64 Apache attack helicopters to destroy Iraqi radar and air defences.

In addition to special forces missions, they also performed in a search and rescue role for coalition airforces in Iraq, Saudi Arabia, Kuwait, Turkey and the Persian Gulf.

After the war, the helicopters played an important role in bringing aid to displaced ethnic Kurds in Operation Provide Comfort, and saw heavy use in Operation Just Cause in Panama.

The unmistakeable twin-rotor CH-47 Chinook is one of the world's most visually striking aircraft. They are extremely versatile, and can operate day and night in virtually all weather conditions.

Chinooks have been in use since 1962

The latest variant Chinook, based on a design which saw service nearly 40 years ago in Vietnam, serves mainly as a long range, medium lift troop-carrier.

The helicopters can carry a large range of internal payloads, including vehicles, artillery, 33 to 44 troops, or 24 stretchers plus two medical attendants.

Specially-adapted Chinooks, known as MH-47E's are used extensively for special forces missions.

These aircraft have larger fuel tanks and more sophisticated radar enabling them to fly at lower altitudes.

Chinooks saw extensive use in the Gulf War in 1991, helping to deploy 5,000 soldiers from the 101st 2nd Infantry brigade.