The United States Air Force and Navy were both seeking new aircraft when Robert McNamara was appointed U.S. Secretary of Defense in January 1961. The aircraft sought by the two armed services shared the need to carry heavy armament and fuel loads, feature high supersonic speed, twin engines and two seats, and probably use variable geometry wings. On 14 February 1961, McNamara formally directed the services to study the development of a single aircraft that would satisfy both requirements. Early studies indicated that the best option was to base the design on the Air Force requirement, and use a modified version for the Navy. In June 1961, Secretary McNamara ordered the go ahead of Tactical Fighter Experimental (TFX) despite Air Force and Navy efforts to keep their programs separate.