Originally organized on 21 July 1916 as Company A, 1st Battalion of Engineers in the California National Guard, the 115th Regional Support Group has been mustered into Federal Service five times under a variety of different designations: Once during the Mexican Expedition, once during World War I, twice during World War (two different predecessor units), and most recently during the Global War on Terrorism. Its longest period of activation under the same designation was from 1971 to 1997 when it was designated as the 115th Support Group (not to be confused with the unit that designated 115th Support or 115th Support [Forward]).
In addition to these deployments, the Group has also served as part of the Kosovo Force on a regular basis since the mid-2000s. To date, the unit has earned credit for participation in six World War I campaigns, seven World War II campaigns—three of them with Arrowheads for taking part in assault landings—and one for the Global War on Terrorism. Unit honors include a Philippine Presidential Unit Citation and a Republic of Korea Presidential Unit Citation (1945-1946).
Currently based at Roseville Armory in Roseville, Califonria, the Headquarters and Headquarters Detachment of the 115th Regional Support Group also commands the 749th Combat Sustainment Support Battalion (headquartered at Benicia Armory) and the 340th Brigade Support Battalion (based at Seaside Armory).
The 115th Regional Support Group Shoulder Sleeve Insignia was approved on 22 November 2005. According to The Institute of Heraldry, the sunburst represents the units World War II campaigns in the southern Philippines, with the scarlet arrowhead an emblem of the Philippine Presidential Unit Citation. Six World War I campaigns are denoted by six fleur-de-lis, and the scarlet border and gold field denote courage and excellence.