Duncannon Fort was originally built in 1587 by Queen Elizabeth I of England as protection against a Spanish landing in the area. The original fort was built as a Star Fort although developed to a certain extent over the next four hundred years.
During the Victorian period it was primarily armed with 68-pdr SB gun and then 80-pdr RML guns, primarily in a coast defence capacity. There was also a mortar battery supporting the coast defence batteries.
During the Napoleonic Wars two Martello Towers were built on the ridge line overlooking Fort Duncannon. Duncannon Martello Tower North and South were intended to deny this high ground to the enemy and prevent him from using it to bombard the land front. These two Martello Towers were built in 1813.
This was a very low priority fortification by the 1860s, hence the armament was very much second line. It was primarily used as a garrison location. There is evidence that first of all there were 68-pdr SB guns mounted here and these were later upgraded to 80-pdr RML guns.