He was honored for heroism during World War II at the battles of Guam (Navy Cross), Bougainville (Bronze Star Medal) and Iwo Jima (Legion of Merit).

He also commanded all Marine forces in the Vietnam War from June to December 1967, and served as deputy director of the Central Intelligence Agency (CIA) from 1969 to 1971.

In June 1941, Cushman reported aboard USS Pennsylvania in San Diego, en route to Pearl Harbor, as commanding officer of the ship's Marine detachment.

Upon his transfer from the Pennsylvania, he joined the 9th Marine Regiment at San Diego as a battalion executive officer in May 1942 and was promoted to major that same month.

In June 1948, he was named head of the Amphibious Warfare Branch, Office of Naval Research, Navy Department, Washington, D.C. From October 1949 until May 1951, he served on the staff of the Central Intelligence Agency (CIA).

Following his return to the United States, he was transferred to Norfolk, Virginia, where he served as a member of the faculty of the Armed Forces Staff College, and in July 1954 became director of the Plans and Operations Division there.

During Cushman's tenure, he saw the last of the Marines leave Vietnam and the peacetime strength fall to 194,000 while still maintaining readiness to act in such emergencies as the Mayaguez incident and the evacuations of Phnom Penh and Saigon.

When his Battalion was ordered to seize and hold a strongly organized and defended enemy strong point which had been holding up the advance for some days on 25 July, Lieutenant Colonel Cushman directed the attacks of his Battalion and the repulse of numerous Japanese counterattacks, fearlessly exposing himself to heavy hostile rifle, machine-gun and mortar fire in order to remain in the front lines and obtain first-hand knowledge of the enemy situation.

Following three days of bitter fighting culminating in a heavy Japanese counterattack which pushed back the flank of his Battalion on 28 July, he personally led a platoon into the gap and, placing it for defense, repelled the hostile force.

By his inspiring leadership, courage and devotion to duty, he contributed materially to the success of the mission with the annihilation of one enemy Battalion and the rout of another, thereby upholding the highest traditions of the United States Naval Service.