This may seem like blasphemy to some, but Popeye started his professional career as a civilian mariner and then Coast Guardsman. The famous sailor did join the Navy, but as of 1937, Popeye was firmly in the Coast Guard. A two-reel feature titled Popeye the Sailor meets Ali Baba's Forty Thieves introduces Popeye serving at a Coast Guard station. The sailor man's creator did not live to see the United States enter World War II, but it was in 1941 that his creation joined the Navy and the legend of Popeye the rough and tumble U.S. Navy sailor was born.
Popeye the Sailor meets Ali Baba's Forty Thieves wasn't Popeye's first feature. He started life as a character in the comic strip Thimble Theater in 1929, a comic actually centered around his off-and-on girlfriend, Olive Oyl. When it became obvious that Popeye was the real star, he made a jump to feature films. In the aforementioned 1937 film is when we see Popeye in the Coast Guard, on guard duty and deploying to intercept "Abu Hassan" (aka Bluto), who is terrorizing the Middle East.
Spoiler alert: Popeye saves the day, but not before telling Bluto to "stop in the name of the Coast Guard."
It was during WWII that Popeye reached his incredible popularity. After enlisting in the Navy in 1941's The Mighty Navy, Popeye's clothing changed and reflected his status as a U.S. Navy sailor, wearing the distinctive white crackerjack uniform. Popeye would remain in uniform until 1978, when new cartoons put him back in his original outfit, with one exception: the white yachting cap he used to wear was replaced with a standard issue Navy "Dixie Cup" cap.
It should be noted that Popeye and Bluto once attempted to join the Army in a 1936 film short called I'm In the Army Now, but they really just ended up fighting in the recruiter's office. Popeye left the office after beating Bluto to a surrender, but without actually joining. Popeye also regularly beats Bluto to the tune of "The Army Goes Rolling Along."
Despite his dedication to service, Popeye never once tried to join the Air Force.