The American Campaign Medal was established with the same Executive Order (9265) used to create the Asiatic-Pacific Campaign and European-African-Middle Eastern Medals in 1942. Its inspiring design—a B-24 overflying a U.S. Navy cruiser and a sinking enemy submarine, with a factory building standing tall in the background—is a reminder of just how great a contribution was made by those stationed on the home front, particularly in helping safeguard U.S. shipping against the German U-boat threat.
Regulations lists five qualifying conditions of service within the American Theater between 7 December 1941 and 2 March 1946. The first two involve permanent assignments, either outside the continental limits of the U.S. or as a member of a ship’s crew sailing in ocean water for either 30 consecutive or 60 cumulative days. Also eligible were those serving outside the continental limits of the U.S. on temporary duty or in passenger status (30 consecutive/60 cumulative days), those who were in active combat against the enemy and were awarded a combat decoration or had formal certification that they’d engaged combat; and those within the continental limits of the U.S. for a total period of at least one year. (The exact definition of "American Theater" can be found Section 5-15(b) of Army Regulation 600-8-22, Military Awards.)
Only one bronze service star is authorized for wear with the American Campaign Medal indicating participation in the antisubmarine campaign. Simply serving on a vessel that encountered enemy submarines is not enough to earn the bronze service start, however: candidates must have been assigned or attached to unit (and present with that unit) that earned credit for the antisubmarine campaign.
The design of the ribbon was approved in 1942, but it was not until December 17, 1948 that the medal was actually awarded, in this case to General George C. Marshall.