On a short walk around Landguard Fort.
Landguard Fort is the site of the last opposed seaborne invasion of England in 1667 and the first land battle of the Royal Marines. The current fort was built in the 18th century, and modified in the 19th century with substantial additional 19th-20th century outside batteries.
You are looking for a camouflaged cache which is placed with the kind permission of Landguard Fort. Please be as inconspicuous as you can when retrieving.
Congratulations to equinaut for being FTF. Very well done.