By the coast path on the edge of a golf course, 500 yards east of The Close, Jaywick Sands.
SEALED. This was a non standard underground post being located in the lower room of a Martello Tower. The entrance on the north side of the tower has been bricked up. The post had dual FSM probe pipes which are still visible on the west and east sides of the tower.
The Martello tower was used for aircraft observation.
Opened in 1961 and closed in 1968.