Frederick Grun was born in March 1923 in Philadelphia, Pennsylvania, the youngest of four children. His father was an insurance broker and remained employed during the Great Depression. Grun was educated through high school in Philadelphia, and remembers that he was a freshman in college when the Japanese attacked Pearl Harbor [Annotator's Note: the Japanese attack on Pearl Harbor, Hawaii on 7 December 1941]. He was returning from tennis practice when a fraternity brother told him the news of the bombings, and Grun said all his friends wanted to "go get those Japs [Annotator's Note: a period derogatory term for Japanese]". But his father advised him to stay in college as long as he could. His two brothers were serving in the Navy and Grun enlisted in November 1942 as a member of the V-12 program [Annotator’s Note: V-12 US Navy College Training Program, 1943 to 1946] that would allow him to finish his college studies. But, in July 1943 he was moved from the Industrial Engineering program at Penn State College [Annotator's Note: then Pennsylvania State College, now Pennsylvania State University, in State College, Pennsylvania] to the Mechanical Engineering program at Cornell University [Annotator's Note: in Ithaca, New York], and as a consequence of the change, his grades suffered. He changed his course of study to Hotel Administration, and finished in June 1943. He attended pre-midshipman school in Asbury Park, New Jersey, where he lived in a hotel, drilled, and took a training course in weaponry. Then he was sent to Notre Dame University [Annotator's Note: University of Notre Dame du Lac in Notre Dame, Indiana] for midshipman school, and was commissioned in August 1944. After a ten day leave [Annotator's Note: an authorized absence for a short period of time], he reported to the 3nd Naval District in New York, then to a Navy base on Long Island [Annotator's Note: Long Island, New York], where he got his first experience as an officer. At the Brooklyn Navy Yard, Grun boarded the HMS Empire Mace, a troop ship headed for Australia.

On 18 August 1944, Frederick Grun left the United States on the HMS Empire Mace along with 200 enlisted men, a number of Australian airmen, and then picked up some Javanese soldiers in Panama. The ship was poorly kept and the food was "terrible," but there was plenty of "booze." They traveled through the Panama Canal, and arrived in the Pacific in the company of six other English ships, escorted by four Canadian frigates. They made a four day stop at Bora Bora [Annotator's Note: Bora-Bora (island), French Polynesia], then got orders to proceed to Finschhafen [Annotator's Note: Finschhafen, Papua New Guinea] "at haste." The cruise took 55 days. From there he went to a naval base at Hollandia [Annotator's Note: Hollandia, Papua New Guinea], and after "scrounging around" a bit, made himself comfortable in quarters. He was assigned to the Officer Messenger Mail Center or OMMS and Registered Public Issuing Office or RPIO, that issued all the secret and top-secret communications for the Navy, including battle plans and communication codes. He remembered the ECM machine [Annotator's Note: ECM Mark II cipher machine], used for coding, and that everything had to be authorized, checked in and checked out. It was there Grun learned to drive a jeep, under British system. It took two months for mail to arrive from the United States, and when he got cookies and cigarettes from home, they were stale. Grun stayed there until the end of January, when he moved to the Philippines on a refrigerator ship, and had the best food in the Navy.

At the end of January [Annotator's Note: January 1945] in Leyte Gulf, Frederick Grun had his first experience with enemy opposition. He reported to the radio center in the "ramshackle" town of Tacloban [Annotator's Note: Tacloban, Leyte, Philippines]; until officers' quarters were built, he lived in a four-man tent and had his laundry done by the natives. He carried on with his duties in secret and top-secret communications for the Navy, and said he spent a lot of time delivering messages and mail in sealed envelopes to ships in Leyte Gulf. When the atomic bombs were dropped, Grun said the reaction was interesting; some guys thought it would be the end of the world. No one really knew what it was, and it was "scary." But Grun felt it was very good news for the Americans. Then, on the night of 15 August, while he was watching an outdoor movie, "all hell broke loose" in the bay: fireworks and gunshots. News had come that the war was over. Grun said they didn't see the end of the movie because they moved to the bar. In December, the Tacloban base was closed and Grun moved to Samar, another island in Leyte Gulf. Secret and top secret mail had disappeared, and Grun was in charge of the office, but because he had little to do, he would tour the primitive island in a jeep. He rarely had contact with the natives, who were operating the mess hall, and the food was terrible. Some of his trips out in the jeep took him to the Seabee [Annotator's Note: members of US naval construction battalions] bases, and a dining adventure. He was on Samar until the middle of January [Annotator's Note: January 1946], when he finally had enough points to go home.

Frederick Grun returned to the United States by way of Hawaii. The four days he spent quartered at Hospital Point in Pearl Harbor, Hawaii was "a ball"; the women were white and the food was wonderful. Although he toured the island, he didn't get to see the USS Oklahoma (BB-37). He observed throughout his service in the war, he was able to visit with fraternity and hometown friends wherever he was stationed. Grun recalled playing bridge during the voyage to San Diego, California, and a warm welcome when he visited his sister in Los Angeles [Annotator's Note: Los Angeles, California]. By taking his first long-distance train trip, he returned to Philadelphia [Annotator's Note: Philadelphia, Pennsylvania] for leave [Annotator's Note: an authorized absence for a short period of time]. Still lacking enough points for discharge, he was assigned to the publications office in Newport, Rhode Island until his discharge on 26 June 1946. When he reflects on the war, he thinks it changed the country. He feels the country had no choice but to enter the war against the tenacious Japanese, and once America became involved, it turned around very quickly.