United States President George W Bush [Images], for his visit to India and Pakistan, leaves Washington on Tuesday on a Boeing Air Force One aircraft.

The presidential air transport fleet, one of a kind, consists of two specially configured Boeing 747-200B's modified to meet presidential requirements.

When the President is aboard either aircraft, or any Air Force aircraft, the radio call sign is 'Air Force One'. Principal differences between the VC-25 and the standard Boeing 747, other than the number of passengers carried, are the state of the art navigation, electronic and communications equipment, its interior configuration and furnishings, self-contained baggage loader, front and rear air-stairs, and the capability for in-flight refueling.

• Complete Coverage: The Bush Visit

While on the aircraft, the President and his staff have access to a full range of services, including communications systems, secure and non-secure voice, fax and data communications, along with access to photocopying, printing, and word processing.

The 'flying Oval Office' has 4,000 square feet of interior floor space, including a conference room, and living quarters for the President and the First Lady and can accommodate 180 people.

The living quarters for the President include an executive suite consisting of a stateroom (with dressing room, toilet and shower) and the President's Office.

A conference/dining room is also available for the President, his family and staff. Other separate accommodations are provided for guests, senior staff, the secret service and security personnel, and the media.

Two galleys provide up to 100 meals at one sitting. Six passenger toilets are provided in addition to a rest area and mini-galley for the aircrew.

The aircraft also has an office that doubles up as a medical facility when necessary, fitted with medical equipment and supplies for minor medical emergencies. It is fitted with multi-frequency radios for air-to-air, air-to-ground and satellite communications.

The colours on the first Air Force One VC-137C were selected by former President John F Kennedy's wife, Jacqueline Kennedy.

The 707s served as Presidential aircraft until they were replaced by 747-200s designated VC-25 in 1990.

According to White House sources, the special aircraft to carry the US President and his delegation was first created in 1944.

Former president Franklin D Roosevelt called for the creation of the Presidential Pilot Office and a C-54 -- dubbed the Sacred Cow -- was put into service for Roosevelt.

For most of the next 20 years, various four-engine propeller-driven aircraft were used for Presidential air travel.

Then came the Independence, a DC-6, which transported former president Harry S Truman from 1947 to 1953.

Former president Dwight D Eisenhower used the Columbine II and Columbine III from 1953 to 1961.

The call sign Air Force One was first used in the 50s and president Kennedy's VC-137 (Boeing 707) was the first aircraft to be popularly known as Air Force One.

In 1962, a C-137C specifically purchased for use as Air Force One, entered into service with the tail number 26000. It is perhaps the most widely known and most historically significant Presidential aircraft.

Tail number 26000 is the aircraft that carried former president Kennedy to Dallas, November 22, 1963, and returned the body to Washington, DC, following his assassination.

Lyndon B Johnson was sworn into office as the 36th president on board the aircraft at Love Field in Dallas.

This fateful aircraft also was used to return Johnson's body to Texas following his state funeral January 24, 1973.

In 1972 president Richard M Nixon made historic visits aboard 26000 to China and to the former Union of Soviet Socialist Republic.

Tail number 26000 was retired May 1998, and is on display at the US Air Force [Images] Museum, Wright-Patterson AFB, Ohio.

Tail number 27000 replaced 26000 and carved its own history when it was used to fly former presidents Nixon, Ford [Images] and Carter to Cairo, Egypt [Images], October 19, 1981, to represent the United States at the funeral of Egyptian President Anwar Sadat.

The first VC-25A -- tail number 28000 -- flew as Air Force One on September 6, 1990, when it transported president George Bush [Images] to Kansas, Florida [Images] and back to Washington, DC.

A second VC-25A, tail number 29000, transported Clinton, Carter and Bush to Israel for the funeral of Prime Minister Yitzhak Rabin. The VC-25A will usher Presidential travel into the 21st century, upholding the proud tradition and distinction of being known as Air Force One.

Historically, several US presidents have flown on Boeing aircraft.

In 1943, president Franklin D Roosevelt flew to Casablanca aboard a Boeing model 314 Clipper. In 1962, Boeing introduced US presidents to modern jet transportation with the introduction of the Boeing model 707-320B.

In all, seven presidents were served by the 707-320B. Today, the chief executive flies aboard a specially configured 747-200B, the newest and largest presidential airplane.

Its capabilities include: longer range for presidential travel, aerial refueling and self-sufficiency at airports around the world.

These aircraft are flown by the Presidential Airlift Group, and are assigned to Air Mobility Command's 89th Airlift Wing, Andrews Air Force Base, Maryland.