The sign is located where the gate to the depot was located.
Needless to say, this was a well guarded site

Text of the sign is as follows:

The U.S. Naval Ammunition Depot, known locally as “The NAD” was the largest of the Navy’s WWII
inland munitions plants, covering almost 49,000 acres of Adams and Clay County farmland.
Ordnance was loaded, assembled and stored from groundbreaking in July 1942 to final closing in June 1966.
By VJ Day in 1945, the NAD employed 10,000 military and civilian workers.
At one point in WWII the site produced nearly 40% of the Navy’s ordnance, including 16 inch shells.
Built at a cost of $71 million, the NAD had 207 miles of railroad track,
274 miles of roads and 2200 buildings, including 10 miles of distinctive “igloo” storage bunkers.
The plant embittered farmers whose land was taken by the government but also produced an
economic boom for the region as Hastings’ population jumped from 15,200 to 23,000 in 1943.
In September 1944 a bomb loading accident killed 9, injured 54 and produced a crater 550 feet long.
The blast was felt 100 miles away and shattered windows for miles around.