The gun tower in Front Street, Pembroke Dock, is commonly referred to as the 'Martello tower'. However, when it was built it was known as a Cambridge Gun Tower.
Emperor Louis Napoleon III was building a Second Empire of France in the 1840's, and was building up an army to facilitate this ambition. It was feared that this would lead to an invasion of Britain. Thus, to protect the very important Royal Naval Dockyard, Lord Palmerston, Prime Minister of England, decided to build defences against a possible invasion and also built numerous towers along the south and east coasts of England.
After all, in 1797 a French force had landed at Fishguard in north Pembrokeshire and was defeated by local forces led by Lord Cawdor - so there was a precedent for attack. To meet this perceived threat, beginning in 1844, no fewer than thirteen forts were built, mostly along the shores of the Milford Haven Estuary - with two infantry barracks a little inland, Scoveston on the north shore and the Defensible Barracks on the south shore. One fort, St Katherine's, was built at Tenby to prevent a possible enemy landing there and prevent their advance over land to Pembroke Dock.
Thus the Front Street gun tower was built in 1851 and is situated on the north eastern corner of the Pembroke Dockyard wall. It formed the third line of defences that an invading fleet would have to run the gauntlet of, if they hoped to reach Pembroke Dockyard.
The tower is built so that the three cannons on the roof, mounted on carriages, can be revolved through 360 degrees. This gave them the ability not only to fire at ships on the sea, but also to turn and shoot at invasion forces in the street outside the dockyard wall, if required. The tower also had some 6-inch (150 mm) howitzers mounted to fire out of embrasures in the walls. Entry to the tower was through the door high in the side. Would-be attackers would need to climb high to enter, and also deal with the tide.
There is another, smaller tower on the south western corner of the dockyard. For added security, there was also the twenty three-gun Star Battery on the north western corner of the dockyard. I should explain that this battery predates the Royal Dockyard by about 50 years. But considering all these defences together, there was a formidable arsenal awaiting an invader. The guns could reach along all sides of the dockyard wall as well as the sea lanes.