The unit was formed 19 October 1923 in the Florida National Guard as the 1st Separate Battalion, Coast Artillery Corps.

The 265th was activated for World War II and served in the harbor defenses of Galveston, Texas, Los Angeles, California, Key West, Florida, Sandy Hook, New Jersey, and Alaska until broken up into battalions in July 1944.

[1] The unit lineage was carried by two antiaircraft battalions organized in 1946, one of which was federalized in Florida during the Korean War.

From February to May 1935, the 2nd Battalion of the regiment was used for riot control in connection with a Veterans Works Project site.

In March 1936, Battery C was used for guard and security duties when President Franklin D. Roosevelt visited Winter Park and Port Everglades, Florida.

[5] In December 1941, the 2nd Battalion was transferred to the HD of Los Angeles, California, where it was stationed until April 1942 when the regiment was ordered to Key West, Florida to man Fort Taylor in the HD of Key West, arriving 18 through 23 April 1942.

The three battalions remained in the Aleutians through the end of the war, and were moved back to the United States via Seattle and inactivated in November 1945.

The unit’s service in Alaska during World War II is denoted by the bezent, a symbol for gold, and the four-pointed polar star.

The diagonal stripe with the nebuly edges, heraldic symbol for clouds, bearing a lightning flash, signifies the Air Defense Artillery's mission.

The barry wavy rounded alludes to water and refers to the regiment’s former Coast Artillery service.