Interested in aviation since childhood, in 1938 Zeamer had joined the M.I.T. flying club based in nearby Norwood. Within a year he was licensed himself with a hundred solo hours in his logbook; he also served as manager of the club. In October 1939, Zeamer applied for the Army Air Corps flight training program and was accepted in December. His entrance to the program was deferred until after his graduation from M.I.T. in June 1940 with a B.S. in civil engineering, specializing in structural engineering. Zeamer began elementary flight school training as a flying cadet in the Chicago School of Aeronautics, Glenview, Illinois, where his leadership skills earned him the position of Captain of Cadets of Class 41-B.

He attended a year of junior college at Culver after graduation, taking on a more rigorous curriculum and attending summer school, allowing him to enter the Massachusetts Institute of Technology (M.I.T.) as a second-year student. In August 1939, after turning twenty-one in July, he received his infantry commission, becoming a second lieutenant in the Army Reserve, assigned to the 312th Infantry, 78th Division.,

In March 1941, he received his wings and a commission in the U.S. Army Air Corps after graduating from basic and advanced flight school at Maxwell Field, Alabama. Initially assigned to the 96th Bombardment Squadron of the 2nd Bombardment Group as assistant engineering officer, Zeamer was transferred to the 63rd Bombardment Squadron, 43rd Bombardment Group, where he served as squadron executive officer. It was there that he first met his future bombardier, Joseph Sarnoski. Sometime during the summer, Zeamer and “all the rest of the second lieutenants” were sent to Patterson Field in Dayton, Ohio, for assisting with the service testing of the new B-26 Marauder by the 22nd Bombardment Group. Following his return to Langley, Zeamer was assigned to the group’s 19th Bombardment Squadron as a co-pilot. On December 8, 1941, the 22nd was transferred from Langley to California to fly anti-submarine patrols and reconnaissance off the west coast of the United States. In March 1942, the 22nd BG was deployed to Australia, where Zeamer flew his first combat mission as a B-26 co-pilot on April 6, 1942. He was promoted to first lieutenant that same month. Still, due to issues of reaction time and aggressiveness on the controls, Zeamer had never checked out as first pilot in the B-26.

With the arrival of his old group, the 43rd, in Australia flying the new “F” model Boeing B-17 Flying Fortress in August 1942, Zeamer sought and obtained a transfer from the 22nd to the 43rd. He reported for duty with the 403rd Bombardment Squadron in Torrens Creek, Australia, on September 22, reuniting with his gunnery trainer and friend from the previous summer, Joe Sarnoski. Lacking any experience in the B-17, Zeamer had to scrounge for flights at first as a self-described “squadron errand boy” before gaining combat experience in October as a substitute copilot and even navigator. Despite having not yet been checked out as first pilot in the B-17, Zeamer flew his first mission as pilot-in-command on November 20, a photoreconnaissance of Simpson Harbor at Rabaul, New Britain. He was awarded the Silver Star for the mission, which also served as his transition to first pilot.

In May 1942, Zeamer was made squadron executive officer, and took up the upgrading of a B-17E, #41-2666, recently acquired from the 8th Photographic Reconnaissance Squadron, for photographic mapping purposes. The aircraft was one of the few in the theater equipped with the trimetrogon camera system, which allowed the creation of photo mosaics for generating maps. The crew replaced the engines, stripped the plane of extra weight, and augmented it with several additional guns, including dual .50 caliber M2 Brownings in both the radio compartment and both waist positions, and a fixed .50 in the nose for Zeamer to fire himself from the control column. Contemporary accounts including the 65th BS morning report for that day as well as Zeamer’s own flight log record it as having sixteen guns total. The aircraft came to be known by the crew as “‘666,” or popularly as “Old 666.”

Around the end of 1942, Zeamer began putting together his own crew, beginning with Sarnoski and squadron navigator Charles “Rocky” Stone. Popular accounts of the crew and its formation refer to them as “screw-offs,” “renegades,” and “misfits,” but are not borne out by the actual record and are either fiction or gross exaggeration. In time they began calling themselves the “Eager Beavers” for Zeamer’s constant volunteering for missions as they came available. An early incarnation of the crew was awarded Air Medals for the sinking of a merchant vessel at Rabaul on January 17, 1943. The bombing of Milne Bay that same day, as well as significant personnel losses to malaria and dengue fever, led to the 403rd being returned to Australia soon after for recuperation. Almost two months of non-combat followed, prompting another transfer for Zeamer, this time into the 65th Bomb Squadron of the 43rd BG, based in Port Moresby, New Guinea, in late March 1943. He was promoted to captain in early April, as well as made squadron operations officer. On April 12 the Eager Beavers flew a mission to Rabaul for which he was awarded an Oak Leaf Cluster to his Silver Star.

In April 1943, Zeamer and the crew had been approached about a solo, 1,200-mile (1,900 km) round-trip photo-mapping mission of the western coast of Bougainville, with emphasis on Empress Augusta Bay where any marine landings would be made. Such maps were considered vital to a future invasion of the island in support of coalescing plans for the reduction of Rabaul. It was presented as a volunteer mission because extended mapping runs would require straight and level flight runs of up to 22 minutes deep in hostile territory.

Zeamer was promoted to major on July 8, 1943, and lieutenant colonel in April 1944. He spent 15 months in recovery, regaining most of the use of his left leg, and returned to active duty at Mitchel Field, New York as a Tactical Field Air Inspector. On January 18, 1945, Zeamer retired from the USAAF on disability.

Colonel Merian C. Cooper, chief of staff to the deputy commander of the Fifth Air Force, Major General Ennis Whitehead, recommended Zeamer be awarded the Medal of Honor, to which Fifth Air Force commander General George Kenney concurred. Zeamer received the award from Chief of the Army Air Forces General Henry H. Arnold on January 16, 1944, at the Pentagon.

He returned to MIT and obtained a master’s degree in aeronautical engineering in 1946. Zeamer then worked for a series of aerospace companies: Pratt & Whitney in East Hartford, Connecticut, followed by Hughes Aircraft in Los Angeles, California, and finally Raytheon in Bedford, Massachusetts. Zeamer moved to Boothbay Harbor, Maine, in 1968, where he enjoyed rowing in the harbor, as he had done in his childhood. He retired in 1975.

Zeamer married in 1949, and with his wife Barbara raised five daughters: Marcia, Jacque, Jayne, Susan, and Sandra. Barbara Zeamer stated that he rarely talked about his wartime experiences or the medal. “I think he didn’t feel he deserved it. He was so close to his bombardier [Sarnoski] and he felt terrible about his being killed.”

Zeamer died in a nursing home at age 88. At the time of his death, he was the last living Medal of Honor recipient of the Army Air Forces. Zeamer’s funeral was held on May 11, 2007, with a burial at Arlington National Cemetery. The governor of Maine, John Baldacci, ordered that flags in the state be flown at half-staff on the day of the funeral.

The 43d Airlift Wing’s headquarters building on Pope Air Force Base was named in Zeamer’s honor in October 2008. Since 2011, the building has been the headquarters of the 43d Airlift Group.

In 2011, Zeamer was selected as the class exemplar of the Class of 2014 at the United States Air Force Academy. His name is now worn on the left sleeve of that class’s athletic jacket uniforms.