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Along with Fort Scammel on nearby House Island, Fort Preble was built to deter attack by a hostile power in the event the United States was considered a belligerent in the ongoing conflict between Great Britain and Napoleonic France. In October 1808, Dearborn ordered a company of soldiers to occupy the fort and instructed them to do whatever was necessary to enforce the Embargo Act against embargo-breaking ships. The embargo was finally lifted in March 1809 when President James Madison took office.
War of 1812
Various units manned Fort Preble during the War of 1812. Among them were elements of the Regiment of Light Artillery, the 21st, 33rd, and 34th Regiments of Infantry, as well as U.S. Volunteers — and in times of crisis local militia. When Winfield Scott and other American soldiers returned from British imprisonment in Quebec, they were landed at Fort Preble. Many of them were emaciated and ill, and some died at the post's hospital.
Soldiers from the fort saw action when Confederate Army raiders entered Portland Harbor on June 26, 1863, aboard a captured ship named Archer. The Confederates captured the United States Revenue Cutter Caleb Cushing the next day, and attempted an escape in an action known as the Battle of Portland Harbor. They were pursued by two steamers carrying soldiers and artillery pieces from Fort Preble, as well as about 100 civilian volunteers. Light wind made escape impossible and the Confederates abandoned the Caleb Cushing in boats after setting the ship on fire. The fire detonated the ship's magazines and the Cushing was destroyed by the explosion. Twenty-three Confederate prisoners were captured and taken to Fort Preble. They remained at Fort Preble until they were transferred to prisoner of war camps.
During this action, Fort Preble was commanded by Major George Lippitt Andrews. (Not to be confused with Brevet Major General George Leonard Andrews.) Andrews was a native of Rhode Island who was appointed lieutenant colonel of the 1st Missouri Infantry at the start of the war. He was mustered out of volunteer service in September 1861 and was commissioned in the Regular Army as the major of the 17th Infantry. He was promoted to lieutenant colonel in 1864. In January 1871 he was promoted to colonel and assigned as commander of the 25th Infantry. He commanded the 25th Infantry for 21 years until he retired from the Army in 1892. 
Post Civil War
In the late 1800s Fort Preble was modernized under the supervision of Army engineer Thomas Lincoln Casey who is best known for overseeing the completion of the Washington Monument. These improvements included added emplacements for large caliber guns behind earthen parapets as masonry walls were found to be ineffective against rifled artillery shells.
In the early 1900s several modern Endicott era coast defense batteries were installed at the fort. These new batteries included two batteries of eight 12-inch mortars, two "disappearing" 6-inch guns and two 3-inch guns.
The fort remained active through World War I and was used during World War II as a naval net depot for net laying ships and as a control station for the Casco Bay degaussing range. Most of the fort's guns were removed in 1942 and the last was removed in 1946.
After World War II it was determined that coast defense forts were obsolete and Fort Preble, along with most forts of its kind, was inactivated in 1950.
In 1952 the fort was sold to the State of Maine and became the campus of the Southern Maine Vocational Technical Institute (SMVTI) which was renamed In 1989 as Southern Maine Technical College (SMTC) and later to Southern Maine Community College (SMCC).
Some of Fort Preble's original early 20th Century brick buildings (including officer's quarters, barracks and a fire station) remain and are in a good state of preservation.
Smith, Joshua M. "Maine's Embargo Forts," Maine History, Vol. 44, No. 2 (April 2009), 143-154.
- Francis B. Heitman. Historical Register and Dictionary of the United States Army, 1789-1903. Vol. 1. pg. 166.
- "U.S.Navy Activities World War II by State". U.S. Naval Historical Center. Retrieved 2012-03-07.