Britain fought three wars against the Dutch in the second half of the 1600s. During the first, from 1652-3, a fort was built in Lerwick, but little is known about it and no trace remains. More is known of the pentagonal fort built here during the Second Dutch War from 1665-7. This cost £28,000 and was built by Charles II's master mason, Robert Milne.
By the war's end in 1667 the walls were still not finished, the cannons were said to be too few and too small, and there was no secure water supply. The fort was abandoned and the Government chose not to place a garrison in Lerwick in the Third Dutch War from 1672 to 1677. So when the Dutch landed in Lerwick in 1673 there was no opposition, and they marked their stay by burning down the barracks in the 1665 fort.
In the late 1770s Britain found itself at war with France, Spain and others during the American War of Independence. In 1781 a new pentagonal fort was built on the site of the 1665 defences, and called Fort Charlotte after the wife of George III. What you see today is largely what was built in 1781.
Fort Charlotte consists of a long seaward-facing side housing up to 12 guns. This directly overlooks Bressay Sound and was built on a rock that dropped sheer to the shore below. The remaining four sides of the pentagon are punctuated by bastions at the corners.
Inside the fort the side overlooking harbour is now a grassy base for the remaining cannons. Some of these point out over the terminus for the Bressay ferry, which operates from the harbourside below.
These days Fort Charlotte has retreated from the sea with the reclamation of land for the harbour and the Esplanade. And more recent building has crowded closely around its landward sides. As a result although the fort has been largely for unchanged in 220 years, it is almost invisible today, and its overall shape can only be seen from the air.
The original buildings inside the fort are also still present. These include the "piles": barrack blocks capable of housing a garrison of 270 men. In the fort's north east bastion still stands the powder magazine, designed to be proof against all forms of accidental ignition, as well as damp and enemy action.
The Fort Charlotte built in 1781 never saw action. It housed a garrison throughout the Napoleonic Wars and was later a base for the Royal Naval Reserve in Shetland. It also served as the town jail and courthouse from 1837-75, and later a custom house and a coastguard station. Today it is in the care of Historic Scotland.