Hidden Pillbox,
Cudmore Grove is located at the eastern end of Mersea Island and covers an area of 38 acres and is owned and managed by Essex County Council. The site comprises an area of grassland; a cliff top grove of oak trees, a small sandy beach and fine views across the Colne and Blackwater estuaries.
The faint remains of an old blockhouse are just visible behind the sea wall. This was built in 1547 to guard the Colne and saw action in 1648 when it was used to starve the Royalists in Colchester for 70 days. After the Civil War it fell into ruins.
Throughout the park you may see many concrete structures, some intact others just shattered concrete on the beach. These are the remains of a coastal artillery battery from World War Two with two 4.7-inch guns, probably of World War One vintage. A Battery Observation Post was the central command position, horizontally-aimed searchlights swept the sea at night from concrete bunkers, and pillboxes guarded the perimeter against ground attack. Three pillboxes still survive, all in good condition.
The two gun casemates now lie as broken concrete on the sands but remain very recognisable from the large ring of gun-holding bolts, the holdfast.
Similarly, the Battery Observation Post is now shattered concrete on the beach, as is one of the two searchlight emplacements, both recognisable from the distinctive shapes. The remaining searchlight emplacement survives as a concrete base on the cliff edge. After 60 years, very few WWII 4.7-inch coastal artillery sites still survive in anything approaching significant form.
The structure of the pillbox has been built into the ground with the machine-gun apertures only just above ground level thus showing a low silhouette to an attacker. There is a central anti-aircraft well with a pedestal, surmounted by a concrete post for holding the machine-gun.
You are looking for a blue container slightly bigger than a 35mm. canister.