Sunday, August 21, 2011

A slight diversion... Maunsell Navy Sea Forts

While doing the research on the last post about the Nab Tower I was interested to see that the unique "floating concrete base and sink it" technology for creating fortifications at sea was re-used in the Second World war... I think most people may have seen these (and to coin a phrase from Mr Kinch on the previous post, they are seriously batty - straight out of "War of the Worlds"):

...lovely photograph, but they are the Army version, and I was more interested in these:

...which are the Navy version.

So the story goes, Maunsell was an architect and went to the MoD at the beginning of WW2 with designs for various forts. The naval fort design was the latest of several that Maunsell had devised in response to Admiralty inquiries. Early ideas had considered forts in the English Channel able to take on enemy vessels.

The forts, built in the Thames estuary and operated by the Royal Navy, were to deter and report German air raids following the Thames as a landmark, and attempts to lay mines by aircraft in this important shipping channel.

There were four naval forts:

Rough Sands (HM Fort Roughs) (U1)
Sunk Head (U2)
Tongue Sands (U3)
Knock John (U4)

The design was a concrete construction; a pontoon barge on which stood two cylindrical towers standing 18 metres in height, 7 metres in diameter. Each tower had 7 floors of which 4 of these floors were used for crews quarters (the wall thickness of the reinforced concrete towers was 9 centimetres) on top of which was the gun platform mounting two 3.75-inch guns. In the centre of the deck was the officers quarters, medical room & kitchen. Mounted on the roof of this living area were two 40 mm Bofors anti-aircraft guns and the operations control room on the roof of which was 2 forms of radar.

So basically a double Nab Tower with a single concrete float, but a lot more armament - but fundamentally the same design. Makes you wonder if Maunsell had studied Menzies original design...

Everything was done in a rush - clearly invasion fever was at it's height - the towers were fitted out at the same time their crews went on board (about 100 men who lived in the legs). Like the Nab they were towed into position (with crews on board) and then sunk to rest on the seabed (with crews on board!)

There were concerns that the same might happen as to the Nab (a list of 3 or 4 degrees) but this didn't happen. Rough Sands was the first fort and was sunk 11th Feb 1942 in 37' water.

Following shows how they were placed...
Interesting... but no more than a diversion!


  1. Very interesting Steve. I knew that Guy Maunsell had been involved in the design of the Mulberry Harbours that were used for the D-Day landings and subsequently, but wasn't aware that he had been involved with these (although the clue is in the name!). By the way, I think he was actually an engineer rather than an architect - and I know this because I work for the company that Maunsell & Partners ultimately became!

    regards WW

  2. Wow! That's a claim to fame - I retract my description of him immediately...!

    I know he was more famous after the war - he didn't start his architects practice until '55 (??) but couldn't find out much about his activities before then.. I'm guessing he was already well known at the start of the war - can't see the MoD spending that kind of money on a plan from an unknown!

  3. Excellent info, thanks for sharing.

  4. I should set a Rocketman battle on something like that! I can just imagine some villain using one as a secret base...

  5. Excellent post. These are very interesting and (it seems to me) eccentric and therefore typically British. I've seen a few similar structures in the Solent protecting Portsmouth.

    Insidentally there is an excellent model of the Army Forts at the Docklands Museum. I wrote about it and posted a picture on my blog when I last visited the museum in June 2009.

  6. Lee - thanks for that - if I'm honest the army one's are the more visually interesting, but don't they look "fragile".. I really wouldn't fancy having to traverse the walkways between the towers in a storm!