The Third Corps was activated on December 18th, 1940, with
Headquarters at the Presidio of Montery, California, and
participated in the defense of the West Coast during the early
years of WW II. Before embarking for the European Theater in
September of 1944, the Corps engaged in four maneuvers, trained
thousands of troops, and prepared elements of 33 different
Divisions for combat.

Third Corps forced a salient in the German lines and earned the
nickname of "Phantom Corps" by constantly hitting the Germans where
they least expected it.

The shoulder patch worn by the III Corps was based upon a
design approved by the AEF on December 3rd, 1918. The three
points of the caltrap (an ancient military device used to
impede cavalry charges) indicate the numerical designation
of the Corps, and the colors blue and white are from the
Corps' distinguishing flag.