The original plans for Fort Mott (initially called the "Battery at Finn's Point") specified eleven gun emplacements for Rodmansmoothbore guns and a mortar battery with six emplacements.[3] Construction was started in 1872; however, only two of the gun emplacements and two magazines in the mortar battery were completed by 1876 when all work stopped due to a general suspension of fort work. The Board of Fortifications, often called the Endicott Board, recommended a comprehensive program of new fortifications in 1885. A new Fort Mott was one of the results, and it was completed by 1902 as part of the Harbor Defenses of the Delaware.
Unusually for US coast defense forts built 1895-1935, Fort Mott was designed to resist a land attack. A parados (basically an artificial hill) and moat were placed behind the gun batteries to impede an assault from the landward side. Also, the fort's four 5-inch guns were in mounts permitting 360° of fire, and were sited to fire on attackers flanking the parados.
The fort had a typical armament for its day, with a few exceptions. The main armament was Battery Arnold (3 12-inch guns) and Battery Harker (3 10-inch guns). These were on disappearing carriages to allow the guns to normally remain hidden from observation from the river. Flanking these were Battery Gregg, with two 5-inch M1900 guns on M1903 pedestal mounts, and Battery Krayenbuhl, with two 5-inch M1897 guns on balanced pillar mounts, each with all-around fire. Battery Krayenbuhl was sited atop the fort's smallest and most unusual battery, Battery Edwards with two 3-inch mine defense guns in large casemates rebuilt from earlier (1872) magazines. These casemated light guns, intended to protect an underwater minefield in the river by driving off minesweepers, were a unique installation in US forts of this era, in which virtually all emplacements were open-top.[4][3]
Battery Arnold was named for Brigadier General Lewis G. Arnold, an artillery officer in the Seminole Wars and the Civil War, who died in 1871. Battery Harker was named for Brigadier General Charles G. Harker, killed at Kennesaw Mountain in the Civil War. Battery Gregg was named for Captain John C. Gregg, killed in action during the Philippine–American War. Battery Krayenbuhl was named for Captain Maurice Krayenbuhl, also killed in action during the Philippine–American War. Battery Edwards was named for Captain Robert Edwards, killed in the War of 1812.[3]
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 12-inch (305 mm) 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.[5] In 1910 the two five-inch guns of Battery Gregg were transferred to Fort Ruger, Hawaii,[6] 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.[3]
The three 10-inch guns of Battery Harker were transferred to Canada in 1941 via Lend-Lease. Two of these remain as of 2014 at Fort Cape Spear, St. John's, Newfoundland. In 1943 Fort Mott was disarmed, losing its remaining three 12-inch guns, the fort being superseded by Fort Miles at Cape Henlopen.[8][3] As with most post-Civil War US coastal fortifications outside the Philippines, Fort Mott's guns were fired only for training and testing, never in battle.
As of 2018, Fort Mott is connected with Fort Delaware and Delaware City by a seasonal passenger ferry operated by Fort Delaware State Park.[9]
