Whitstable to Red Sands Sea Fort Coast

Whitstable. Famous for its oysters.

There's been a festival of one kind or another to celebrate

the local catch ever since the Romans first invited themselves over

around 2,000 years ago.

'That's 2,000 years of coming down to the sea for pleasure,

'for nourishment...'

Oh, my goodness! It's Moby Dick in here. OK, down the hatch.

'..To build stuff.'

Right, you show me what to do.

Hereabouts the children don't make sandcastles,

they build something called a grotter,

tottering towers made from oyster shells.

No-one's quite sure how it started, but the construction

usually coincides with the ancient feast day of St James in July.

At the end of it, these miniature shrines are offered up to the sea

to be washed away by the tide.

We do seem to have a tradition of building strange stuff on the coast.

We're six miles offshore, north of Whitstable.

Aren't these fantastic? From this angle they almost look

as if they're moving, there's a hint of every robot monster

that you ever saw in a sci-film, but more than anything

to me, they look like the Martians in the War Of The Worlds.

This group of odd looking towers is the Red Sands Sea Fort.

Built in 1943, it was a late addition to London's air defences,

the vision of engineer Guy Maunsell.

As building offshore in wartime was dangerous,

Maunsell had to pioneer a new technique of construction.

Each of the 750-ton towers was assembled on land,

then floated out on pontoons and dropped onto the seabed.

When in place, the individual towers of the fort

were linked by aerial walkways.

The fort housed up to 265 men,

stationed here for a month at a time.

This is a very strange place.

On the one hand, it's all this rusted metal and rivets,

it feels like the rusting hulk of an old battleship,

but then you come in here, and there's beds,

because since the war it's used intermittently as a radio station.

It just adds to the sense of it being, I don't know,

vaguely haunted out here, strange place.

This was one of three forts built in the Thames Estuary.

They were the result of hard lessons learnt early in the war

when German bombers had used the Thames

as a route to navigate to the capital.

From the top of the towers anti-aircraft guns had a clear shot

at planes trying to get to London.

They destroyed 22 of them as well as 30 flying bombs.

For Maunsell, it was an engineering triumph.

Every now and again you can feel the whole thing move,

and that's because, 750 tons or not, the strength of the fort

comes from the fact that the legs can move, they can settle

into the constantly shifting sand,

and it can roll with the waves and the wind much like a tree does.

They say that even if one of the legs was blown out,

the individual tower would still remain standing.

I don't really fancy trying that myself.

Maunsell's sea fort design was to serve Britain

one more time after the war.

In 1955, the very first offshore drilling platform in the North Sea

was adapted from his tower design,

a clear inspiration for the oil rush ten years later.