On and extending at the angles of a yellow trefoil which is within an imaginary 2 inch (5.08 cm) circumscribing circle, three red projectiles 1 1/8 inches (2.86 cm) in length and 3/8 inch (.95 cm) in width, with points out, all on an olive drab circular background 2 7/8 inches (7.30 cm) in diameter.
The colors used are associated with the Coast Artillery. The three projectiles and trefoil indicate the original unit's numerical designation.
The shoulder sleeve insignia was originally approved for the Third Coast Artillery District on 12 June 1941. It was redesignated for the Chesapeake Bay Frontier Defense Sector on 23 March 1942.