President Barack Obama salutes as he boards Marine One helicopter at the White House in Washington.(AP)

Marine One is the sign used when President is on board

Marine One is the call sign used when the President is on board one of the HMX-1 Marine helicopters. The primary presidential helicopter is the Sikorsky VH-3D (Sea King).

HMX-1 was established in December 1947

HMX-1 was established in December 1947 as an experimental unit to test and evaluate helicopters and tactics.

HMX-1 provides all helicopter transportation for the President both overseas and within the continental United States.

In addition, HMX-1 provides helicopter transportation for the Vice President, members of the President's Cabinet, and foreign dignitaries as directed by the White House Military Office.

HMX-1 also provides helicopter emergency evacuation

HMX-1 also provides helicopter emergency evacuation and other support as directed by the Commandant of the Marine Corps.

HMX-1 is tasked with the Operational Test

HMX-1 is tasked with the Operational Test and Evaluation of US Marine Corps assault helicopters and related equipment.