Delaware's 261st Coast Artillery Battalion was a harbor defense unit, charged with defending the Delaware bay. Shortly after entering Federal service, it went into "temporary" bivouac on the sand dunes at Camp Henlopen.

Before the battalion was through, the bivouac had become the $20,000,000 Fort Miles, the most modern and best equipped coast defense installation on the Atlantic Coast, and the 261st played a major part in setting up and manning the fort. It also set new gunnery records while there.

As a unit, the 261st did not see action in World War II, but by late 1943 most of the original National Guard members were in combat zones. Some had transferred out of cadre personnel for the many new units being formed - one Coast Artillery unit went to Greenland, other Field Artillery units joined in the expanding efforts in Europe and the South pacific. Almost all of the men of the 261st saw overseas service in other units.

To replace the National Guard while it was in Federal service, a State Guard was organized in early 1941, and under command of Colonel J. Paul Heinel, it rendered dedicated and effective service until 1947, when a reorganized National Guard could resume responsibility. Originally organized as a single battalion, it was later expanded to a regiment of two battalions - eight companies - made up of men too old or young for active military service, or with minor disabilities that kept them from Army service. At annual camps from 1942 to 1946, the State Guard continually won praise from Army Service Command representatives for its military proficiency.