Merlyn was born on the 29th of June, 1934, in Greenville, Iowa, and his parents were farmers and his mother was a teacher. He was able to graduate with honors from high school at the age of 16 and he went on to attend Iowa State University. Merlyn joined the Air Force in 1953 and by the time he turned 20, he had attended an aviation cadet training program and received his commission. He was a navigator on C-124 Globemaster transports for a few years and eventually earned his pilot’s wings in 1960.

Merlyn was married to Jorja and they had two children and he managed to return to college and earned a degree in business from the University of Nebraska. Prior to deploying to Vietnam, he had been a fighter pilot in Germany and in October of 1966, Merlyn’s squadron was based in Thailand in support of the Vietnam War. He was 33 years old when he went on his 78th combat mission and it was his actions on the 10th of March, 1967, that would earn him the Medal of Honor. The citation reads:

Maj. Dethlefsen was one of a flight of F-105 aircraft engaged in a fire suppression mission designed to destroy a key antiaircraft defensive complex containing surface-to-air missiles (SAM), an exceptionally heavy concentration of antiaircraft artillery, and other automatic weapons. The defensive network was situated to dominate the approach and provide protection to an important North Vietnam industrial center that was scheduled to be attacked by fighter bombers immediately after the strike by Maj. Dethlefsen's flight. In the initial attack on the defensive complex the lead aircraft was crippled, and Maj. Dethlefsen's aircraft was extensively damaged by the intense enemy fire. Realizing that the success of the impending fighter bomber attack on the center now depended on his ability to effectively suppress the defensive fire, Maj. Dethlefsen ignored the enemy's overwhelming firepower and the damage to his aircraft and pressed his attack. Despite a continuing hail of antiaircraft fire, deadly surface-to-air missiles, and counterattacks by MIG interceptors, Maj. Dethlefsen flew repeated close-range strikes to silence the enemy defensive positions with bombs and cannon fire. His action in rendering ineffective the defensive SAM and antiaircraft artillery sites enabled the ensuing fighter bombers to strike successfully the important industrial target without loss or damage to their aircraft, thereby appreciably reducing the enemy's ability to provide essential war material. Maj. Dethlefsen's consummate skill and selfless dedication to this significant mission were in keeping with the highest traditions of the U.S. Air Force and reflect great credit upon himself and the Armed Forces of his country.

The defensive complex mentioned in the citation was the Thai Nguyen Steel Plant that was about fifty miles north of Hanoi and was very important to the North Vietnamese. Merlyn and three other planes were to fly in as a distraction so that a second strike force could come in and destroy the plant without taking heavy fire. Because he had not dropped his ordnance when first attacked, he was able to complete the mission and bombers were able to carry out their mission successfully.

Merlyn’s plane was so badly damaged that it had to land at Udorn Royal Thai Air Force Base to get patched up so that it could then make it back to his home base. When his deployment was done, he returned to the States and became a pilot instructor at Vance Air Force Base and on the 1st of February, 1968, Merlyn received the Medal of Honor from President Johnson in a ceremony at the White House.

Merlyn went back to school again, this time earning a Master’s degree in psychology from Troy State University, and retired from the Air Force in July of 1977 at the rank of Colonel. He ran a small medical equipment business in Fort Worth, Texas until the 14th of December, 1987. Merlyn Hans Dethlefsen was 53 years old when he died and he is buried in Arlington National Cemetery: Section 65, Lot 1626.