With the development of the Endicott System, coastal fortifications entered the 20th century at Fort Washington, where eight reinforced concrete batteries were built near the old fort to mount modern artillery and many support buildings, including officer and enlisted quarters, were erected. The system used several types of weapons intended to repel all classes of enemy naval vessels: 6-inch and 10-inch disappearing rifles could reach enemy battleships and cruisers 6 to 7 miles downriver; searchlights were added in the early 1900s to spotlight vessels attacking at night; eight 12-inch seacoast mortars could lob 700-pound shells almost vertically through the lightly armored decks of battleships and cruisers; submarine mines anchored in a predetermined pattern in the river could be fired electrically from shore; and small caliber rapid-fire guns mounted near the river could protect the minefield from enemy destroyers and minesweepers. In 1921, after Fort Washington was no longer needed as a coastal defense, it housed part of the 12th U.S. Infantry Regiment.