The 6-inch Rapid Fire Armstrong Rifle was purchased from England in 1898, because the United States did not have the capability to produce a small, rapid-fire weapon for the defense of its principal harbors.  The advent of the Spanish-American War brought about the need for such weapons in this area due to the close proximity of Cuba to Florida. The installation was completed as a part of the armament of Ft Dade, on Egmont Key, on December 10, 1898.

These weapons, weighing 17 tons each, were breech-loading, utilizing shell cases that were refillable with 13 ½ pounds of powder.  The projectile weighed 100 pounds and had a maximum range of 10,000 yards (5.68 miles) reaching as target in 28.12 seconds.