During World War II he commanded an engineer battalion on Ascension Island in the South Atlantic, and he supervised the construction of a military airfield there that became a key refueling point for transatlantic flights to Africa.

From 1960 to 1963 he was one of the three federally appointed commissioners that governed the District of Columbia and initiated the construction of the Washington Metro railway and subway system.

As chairman of the District's zoning commission, he participated in early debates over the proposals to build a bridge near the Three Sisters Islands in the Potomac River.

[1] Following his junior high school year he worked for Western Union during the summer, and after graduation he joined it full time as a teletype operator.

One day he saw an advertisement for a competitive examination for entry to the United States Military Academy at West Point, New York, and he took it.

[1] Clarke entered West Point on 1 July 1933.He graduated fourth in the class of 1937 on 12 June 1937 and was commissioned as a second lieutenant in the United States Army Corps of Engineers.

He was assigned to the 5th Engineer Regiment at Fort Belvoir, Virginia,[6] While at West Point he met and courted Isabel Van Slyke, who worked for the League of Nations Association as a research assistant.

[10] In August 1940, Clarke assumed command of Company C of the 15th Engineer Battalion, which was based at Fort Bragg, North Carolina,[10] as part of the 9th Infantry Division.

[10] After the Japanese attack on Pearl Harbor that brought the United States Into World War II, he attended an abbreviated wartime Command and General Staff College course at Fort Leavenworth, Kansas.

In February 1942, his battalion sailed to Ascension Island in the South Atlantic, where he supervised the construction of a military airfield there that became a key refueling point for transatlantic flights to Africa.

He was engaged in long-range logistical planning for communications, airfield and port construction, road and railway rehabilitation, and hospitals.

The Manhattan Project ended on 31 December 1946, but Clarke stayed on at Hanford as the Atomic Energy Commission's area operations officer until September 1947.

He was then transferred to Sandia Base near Albuquerque, New Mexico, as executive officer of the Armed Forces Special Weapons Project at the personal request of its commander, Lieutenant General Leslie R. Groves Jr.. At Sandia he oversaw the construction of new facilities and the establishment of training programs for weapons assembly teams.

He briefly served as head of the Construction Management Branch of G-4, where he was concerned with the funding, manufacture and emplacement of Nike missile batteries.

He then became head of the Production Mobilization Branch, with responsibility for the readiness of the national munitions and armament industries, and was special assistant to Palmer's successor, Lieutenant General Carter B.

In the early 1960s, he participated in talks that led to the compact agreement for construction of the Washington Metro railway and subway system.

He established a ten-month training course to prepare field officers for command at the battalion level and for duty on staffs of divisions and higher formations.

[23] When Clarke retired from the Army on 1 July 1973 after 36 years of service,[13] he was the last member of the West Point class of 1937 on active duty.