 New defenses were recommended for 27 harbors and river estuaries; most of the board's recommendations were implemented in what was often called the Endicott Program.This included new rifled guns ranging from to , most of them to be on disappearing carriages in new reinforced concrete emplacements faced with earth.The combination of earth-faced emplacements and disappearing carriages was intended to conceal the guns from an enemy; the airplane had not been invented yet.