Fort McRee was one of three major installations constructed by the United States to strengthen defenses at Pensacola Bay following the War of 1812.
Its construction lasted from 1834 to 1839; the facility was a three-tiered fort and a detached water battery close to sea level.
However, General Simon Bernard's plans for the fort called for 8 of the casemates to be used as quarters and store rooms, and 2 of the 8 were to be used as powder magazines.
It is likely that many of these guns were not in place for some time due to several issues, the most important of which was a problem with rot beginning in the second tier wooden decking.
With less than 50 men to occupy all three fortifications in Pensacola, First Lieutenant Adam J. Slemmer (the senior Army officer present) decided to concentrate his small force in a more defensible location.
Over 9 and 10 January 1861, his garrison spiked the guns of Barrancas and McRee then moved across the bay to Fort Pickens.
The move was a timely one as on 12 January, Florida and Alabama militia arrived and took control of the evacuated fortifications.
Near the end of the year, manning stood at about 7,000 men on the Confederate side opposed by 2,000 Union soldiers around Fort Pickens.
[2] On 9 October 1861 the commander of Confederate forces in Pensacola, General Braxton Bragg, ordered an assault on Fort Pickens that was ultimately unsuccessful.
However, the combined efforts of the two ships eventually led to the suppression of fire by an adjacent battery early in the afternoon with the guns of Fort McRee falling silent by 5pm.
The commander of Fort McRee, Colonel John B. Villepique, advised that his position was heavily exposed on most sides and that half his weapons had been dismounted and their powder stores unprotected.
Large chunks of the wall were blown away while other portions had holes shot clean through by the cannon shells.
[2] When Confederate forces abandoned Pensacola in May 1862, they burned Fort McRee and several other buildings in the area believed to be of strategic value.
This request was denied by the Army Corps of Engineers on the basis that the remaining bricks were worth more to the War Department as a source of material for repairing Fort Barrancas and structures at the nearby Navy yard.
[2] With the completion of the Endicott Board and the subsequent renewed interest in strengthening the coastal defenses of the US, activity returned to Fort McRee.
It was named Battery Slemmer in honor of the Union officer who evacuated Pensacola at the start of the Civil War.
[2] Batteries Slemmer and Center were manned by members of the US Army Coast Artillery Corps, with between 50 and 100 personnel who were rotated from Fort Barrancas.
With America's entry into World War I in 1917, the guns of Battery Slemmer were removed and sent to Europe for mounting on railway cars.
However, due to its location on a site accessible only by foot or boat, Fort McRee was left to the elements.