Fort Mott, along with Fort Delaware and Fort DuPont, became obsolete as the principal defensive installations on the Delaware River with the construction of Fort Saulsbury, near Slaughter Beach, Delaware, shortly after World War I. Fort Saulsbury had four guns on long-range barbette carriages and was sited to engage the enemy much further down the estuary than the earlier forts. The Harbor Defenses of the Delaware was one of the most extreme examples of coast defense forts being built further seaward as gun ranges increased. In 1910 the two five-inch guns of Battery Gregg were transferred to Fort Ruger, Hawaii, and in 1918 the similar guns of Battery Krayenbuhl were removed for potential service as field guns on the Western Front. In 1920 the unique Battery Edwards was disarmed as part of a general removal from service of the 3-inch gun M1898.