In case you really don’t know, “Semper Fi” is an affectionate abbreviation of the motto of the United States Marine Corps. The full Latin phrase is semper fideles, which means “always faithful” or “always loyal”. The USMC have had “Semper Fideles” as their motto since 1883. It’s also the name of one of their best-known marches, authored by John Phillips Sousa.
Semper Fidelis isn’t exclusively owned by the Marines though. It’s been the motto of towns, families and other military organizations going back centuries. Abbeville (France), Exeter (England) and even White Plains NY all tout this motto. Many military organizations around the world claim to be Semper Fideles, including the US Army’s own 11th Infantry Regiment, based at Fort Benning.
It must be said, however, that while Semper Fidelis can be claimed by many, Semper Fi can really only refer to the pride of being a United States Marine.