VXX is a procurement program to replace aging Marine One helicopters that transport the President of the United States. The current VH-3 helicopters have aging airframes, having entered service with U.S. Marine Corps Marine Helicopter Squadron One (HMX-1) in 1963. The VH-3D replaced the VH-3A by 1976. The smaller VH-60N was ordered beginning in 1989.[citation needed]