Captain America #109 (1969)

Captain America has a visit from Nick Fury, and tells the S.H.I.E.L.D. operative an old war story from 1944, in which he and Bucky worked together to take down a Nazi coastal gun control unit so that Allied Forces could launch another beach assault in the war effort. This story once more leads Cap into his lamentations over Bucky's death, and how guilt ridden he is that he managed to outlive his young partner. Fury is not that sympathetic about Bucky's loss and points out that Captain America at least still has his youth and fighting spirit and that even back during World War II he made Fury's Howling Commandos look like amateurs in battle. Captain America explains to Nick that in order for Captain America to live, it had to come at the sacrifice of Steve Rogers, and begins telling the tale of how he became Captain America: In the early days of World War II, before America got involved in the war, frail Steven Rogers attempted to apply for the military. However, he would not pass his physical, and he would be rejected when he would attempt to volunteer. Overhearing this conversation was a military Colonel, who would offer him the chance to test a new experiment that might make him fit for joining the army and fighting in the war. As Steve Rogers was led away, off America's shores a Nazi submarine would get past America's sea mine defense and release a spy who was about to infiltrate the secret experiment called Operation: Rebirth. Under absolute secrecy, Steve Rogers is taken to an antique shop which was really a front for the secret operation and eventually he would meet the scientist behind the super-soldier serum: Professor Reinstein. Before an audience of military brass (and the Nazi spy), Rogers would be injected with the serum and then exposed to Vita-Rays that would speed up the process of transforming Steve Rogers from a frail young man into that of man at the peak of human perfection. After the experiment Reinstein would be shot by the Nazi spy and in his death the secret behind the serum would be lost. Steve would then attack and ultimately kill the Nazi spy in stopping him from assassinating him as well. With America's only super-soldier, the US army would set up Steve as Captain America and have him fight crime in America until the United States officially entered World War II. They would set Steve up under the command of Sgt. Duffy, and under orders of the War Department, Steve was to keep his double identity a secret. To cover for this, Steve would act as a first class bungler when not operating as Captain America. Steve would make fast friends with Bucky Barnes, his platoon's mascot who's father was killed in the line of duty. It would be Bucky who would first learn Captain America's true identity and use that information to force Cap to allow Bucky to be his sidekick. Cap finishes up his story that by the war's end Bucky's luck ran out and he died. With his story done, Steve thanks Nick for letting him get things off his chest. As Fury walks out the door to go and resume his work at S.H.I.E.L.D., he tells Cap that losses like that are hard to forget, but recommends that Steve go out there and have a few laughs. With Fury gone, Steve considers that perhaps after all these years, he's forgotten how to.