The 51st Signal Battalion was constituted on July 1, 1916 into the Regular Army as the 5th Telegraph Battalion, Signal Corps. The unit was later activated on July 12, 1917 at Monmouth Park, New Jersey. On October 1, 1917, the battalion re-designated as the 55th Telegraph Battalion. Soon thereafter, the battalion deployed to France and joined the American Expeditionary Force. During World War I, the battalion participated in three campaigns – Lorraine 1918, St. Mihiel and Meuse-Argonne.

The battalion returned to New York on June 27, 1919 and moved to Camp Vail, New Jersey. The battalion was re-designated on March 18, 1921, as the 51st Signal Battalion. On August 5, 1925, the battalion returned to Fort Monmouth, New Jersey and would remain there until after World War II. The 51st Signal Battalion received additional training at Fort A.P. Hill, Virginia, Camp Blanding, Florida, and Camp Stewart, Georgia prior to deploying for Europe on April 16, 1941. On March 4, 1943, the 51st headed to North Africa and staged and participated in the Invasion of Sicily, followed by a mission to provide communications support to forces arriving in Italy in October 1943. For its service in World War II, the battalion was credited with five campaigns and received the Meritorious Unit Commendation.