Fort De Soto was constructed on Mullet Key in Tampa Bay beginning 1898 (Location of Fort De Soto). Work continued until 1903, when the last guns were mounted and test fired. Fort De Soto, along with Fort Dade on Egmont Key were built to protect Tampa Bay from naval attack. The fortifications protecting Tampa Bay were not originally part of the system planned by the Endicott Board, however, concern about the protection of Tampa Bay during the Spanish-American War lead to its addition to the construction program.
The most notable aspect of Fort De Soto as it is today are the 4 remaining 12-inch M1890-M1 seacoast mortars of Battery Laidley. Originally, 8 mortars were emplaced at Fort De Soto, however, 4 were removed in 1917 for emplacement elsewhere. The fact that the remaining weapons were not removed by the army either after the post was deactivated during the 1920's, or during World War II, when the island was used as a bombing range is extremely surprising. These mortars are the only weapons of their kind remaining in the continental U.S.
The only other battery located at Fort De Soto was Battery Bigelow, a 3-inch rapid fire battery. The rapid fire batteries were needed to prevent an opposing force from sending in small, maneuverable craft to remove underwater minefields, or torpedo boats to attack vessels in the harbor, either of which would be difficult to engage with the large caliber weapons, such as the mortars of Battery Laidley. This battery was badly damaged by storms during the 1920's, and is presently in the surf, with little remaining.
The mortars of Battery Laidley were originally arranged with 4 mortars in each "pit". When 4 of the mortars were removed in 1917, the two mortars in the front of each pit were retained.
A closer view of a mortar, in its firing position. Note the angle (from 45 to 65 degrees elevation) at which shells were fired, allowing the vertical wall protecting the emplacement to be very close to the mortar itself.Continue
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