Unknown structure/possible AA site- istead rise, gravesend - march '11

Noticed this place on the way home from istead rise one time, noticed a odd looking structure which intern i decided to investigate

The main part is round with several out buildings, looks like theres possible underground section but its filled in, further along the field there was some more concrete ruins with another possible underground section.

No history on this place but possibly AA gun post to defend gravesend airport

Looks more like a water tank to me. The breach in the wall could be to ensure it does not fill up with rain water.

Seconded, possibly a filter bed - maybe part of the airfield water/waste system?

Thirded! That was the first thing I thought too, looking at the circular bed.

Probably a reservoir, or even a treatment bed. Where is the structure in picture 13 in relation to the circular structure?
GDZ

Nice first post and good to see youve had a good go at researching the location too
Look forward to some more.

SK

I vote reservoir too - the pipe leading in to it suggests that to me