G-2 refers to the military intelligence staff of a unit in the United States Army. It is contrasted with G–1 (personnel), G–3 (operations), and G–4 (supply). These "G" sections have counterparts in other branches of the service, the U.S. Navy using an N– designation and the Joint Staff the prefix J.
G-2 intelligence played an important role during World War II, both aiding fighting forces and in special missions such as those of T-Force and Operation Alsos.
G-2 intelligence gathering and interpretation traces its history to the American Revolution:
The G– system, as well as the basic structure of military intelligence and even the concept of an army general staff, are surprisingly modern creations. Although George Washington proved shrewd at gathering and using intelligence in the American Revolution, it was only in 1885 that the army formally instituted its Division of Military Information under the Adjutant General's Office.
European armies had meanwhile adopted the G–designations, which originated in France. In 1903, the U.S. Army implemented the concept of a permanent general staff, and with it the four sections pioneered in Europe. The Division of Military Information thus became G–2.
Interest in military intelligence grew during World War I, which saw the formation of an intelligence division under the War Department General Staff. The army also instituted the use of staffs that included intelligence officers all the way down to the battalion level. This emphasis on military intelligence, however, subsided after the armistice.
The army treated the work of G–2 as a function that any officer could fill, hence there was no need for any permanent military intelligence organization. In 1950, General Dwight D. Eisenhower commented in an address to the War College, "I think that officers of ability in all our services shied away from the intelligence branch in the fear that they would be forming dimples in their knees by holding teacups in Buenos Aires or Timbuctoo."
The Military Intelligence Service was formed during World War II. In time, this evolved into the The Military Intelligence Corps, one of the basic branches of the United States Army.