UXB on the Wild Shore

Before I start my exams on Friday, in a kind of pilgrimage of sorts, I went for a walk on Shoeburyness sea front only to be faced by a long fence:

(Taken using the steam-driven mobile and thus the poor quality). There were signs on the fence explaining it's purpose:

Locals know that Shoeburyness was the army ordnance testing range for some years and still has a military/M.o.D. presence. Then again, the Luftwaffe used the river to guide them into London and could have dropped something on the way back; or it could be something related to the ammunition ship, the Richard Montgomery, sunk off the Isle of Sheppey, although that's mostly opposite Thorpe Bay, so that's alright, then.