0:00:33 > 0:00:38Whitstable. Famous for its oysters.
0:00:38 > 0:00:41There's been a festival of one kind or another to celebrate
0:00:41 > 0:00:45the local catch ever since the Romans first invited themselves over
0:00:45 > 0:00:47around 2,000 years ago.
0:00:48 > 0:00:54'That's 2,000 years of coming down to the sea for pleasure,
0:00:54 > 0:00:57'for nourishment...'
0:00:57 > 0:01:00Oh, my goodness! It's Moby Dick in here. OK, down the hatch.
0:01:02 > 0:01:04'..To build stuff.'
0:01:04 > 0:01:07Right, you show me what to do.
0:01:07 > 0:01:09Hereabouts the children don't make sandcastles,
0:01:09 > 0:01:13they build something called a grotter,
0:01:13 > 0:01:16tottering towers made from oyster shells.
0:01:18 > 0:01:21No-one's quite sure how it started, but the construction
0:01:21 > 0:01:27usually coincides with the ancient feast day of St James in July.
0:01:29 > 0:01:33At the end of it, these miniature shrines are offered up to the sea
0:01:33 > 0:01:35to be washed away by the tide.
0:01:36 > 0:01:42We do seem to have a tradition of building strange stuff on the coast.
0:01:45 > 0:01:49We're six miles offshore, north of Whitstable.
0:01:51 > 0:01:54Aren't these fantastic? From this angle they almost look
0:01:54 > 0:01:58as if they're moving, there's a hint of every robot monster
0:01:58 > 0:02:00that you ever saw in a sci-film, but more than anything
0:02:00 > 0:02:03to me, they look like the Martians in the War Of The Worlds.
0:02:05 > 0:02:09This group of odd looking towers is the Red Sands Sea Fort.
0:02:09 > 0:02:14Built in 1943, it was a late addition to London's air defences,
0:02:14 > 0:02:18the vision of engineer Guy Maunsell.
0:02:22 > 0:02:25As building offshore in wartime was dangerous,
0:02:25 > 0:02:28Maunsell had to pioneer a new technique of construction.
0:02:28 > 0:02:33Each of the 750-ton towers was assembled on land,
0:02:33 > 0:02:38then floated out on pontoons and dropped onto the seabed.
0:02:38 > 0:02:41When in place, the individual towers of the fort
0:02:41 > 0:02:45were linked by aerial walkways.
0:02:46 > 0:02:49The fort housed up to 265 men,
0:02:49 > 0:02:53stationed here for a month at a time.
0:02:53 > 0:02:55This is a very strange place.
0:02:55 > 0:02:59On the one hand, it's all this rusted metal and rivets,
0:02:59 > 0:03:01it feels like the rusting hulk of an old battleship,
0:03:01 > 0:03:05but then you come in here, and there's beds,
0:03:05 > 0:03:10because since the war it's used intermittently as a radio station.
0:03:10 > 0:03:14It just adds to the sense of it being, I don't know,
0:03:14 > 0:03:18vaguely haunted out here, strange place.
0:03:21 > 0:03:25This was one of three forts built in the Thames Estuary.
0:03:25 > 0:03:29They were the result of hard lessons learnt early in the war
0:03:29 > 0:03:32when German bombers had used the Thames
0:03:32 > 0:03:35as a route to navigate to the capital.
0:03:38 > 0:03:42From the top of the towers anti-aircraft guns had a clear shot
0:03:42 > 0:03:44at planes trying to get to London.
0:03:44 > 0:03:50They destroyed 22 of them as well as 30 flying bombs.
0:03:50 > 0:03:53For Maunsell, it was an engineering triumph.
0:03:56 > 0:03:59Every now and again you can feel the whole thing move,
0:03:59 > 0:04:03and that's because, 750 tons or not, the strength of the fort
0:04:03 > 0:04:07comes from the fact that the legs can move, they can settle
0:04:07 > 0:04:09into the constantly shifting sand,
0:04:09 > 0:04:13and it can roll with the waves and the wind much like a tree does.
0:04:13 > 0:04:18They say that even if one of the legs was blown out,
0:04:18 > 0:04:22the individual tower would still remain standing.
0:04:22 > 0:04:25I don't really fancy trying that myself.
0:04:29 > 0:04:32Maunsell's sea fort design was to serve Britain
0:04:32 > 0:04:36one more time after the war.
0:04:38 > 0:04:42In 1955, the very first offshore drilling platform in the North Sea
0:04:42 > 0:04:45was adapted from his tower design,
0:04:45 > 0:04:49a clear inspiration for the oil rush ten years later.