However, not all such projects have been forgotten and some are still in existance to this day,long after there design life, to remind us of the effort made by those civilians during the dark days of warOne project in particular concerned the construction of a number of fortresses on the banks of the Thames at the Red Lion Wharf site, now occupied by the defunct Northfleet Power Station, but then occupied by Holloway Brothers Ltd.
At the time the work was considered to be very advanced, due to the new ideas and techniques employed. In total, the work on the fortresses cost the nation approximately £33,000,000 at 1994 prices but very little evidence exists at Northfleet to commemorate this unique achievement.
The fortresses were designed by Mr Guy Maunsell a notable architect of the period, responsible for a number of difficult and pioneering civil engineering projects pre-war. Among these were the repair and overhaul of the MenaiStraights Bridge, the widening of Putney Bridge over the River Thames and the building of the Storstrom bridge in Denmark in 1934, then the longest bridge in Europe, with a length of 10,535ft..
Working for the Admiralty, Maunsell initially designed the Naval Fort. Weighing some 4,500 tons each, four of these were sunk in position in the Thames Estuay in 1942 and proved so successful that he was then asked to produce a solution for the Army offshore anti aircraft defences . For this he produced an entirely different design comprising of seven seperate fortresses positioned in clusters, to represent an army unit as dispersed and utilised on land. Three such clusters were sunk in the Thames Estuary and a similar amount, constructed by the Cleveland Bridge and Engineering Company, at Bromborough, were sunk in the Mersey Estuary.
In 1939 with war clouds looming, Guy Maunsell submitted to the Admiralty an idea for a submersible observation post. The vessel resembled a bottle in shape and was 67' 6"overall and weighed 160 tons. Approximately 20 feet remained above water and atop the vessel a crows nest was to be manned 24 hours a day.
It was suggested that it be built in large numbers, at a cost of £150,000 each , at 1994prices, and be placed around the coast line some 10 miles off shore. It was to have a crew of five men who were to spend 14 days aboard before being relieved.During their occupation, the crew were to observe enemy movements of shipping and aircraft as well as listen out for submarine activity.
All movements were to be transmitted by radio to a shore location. In the event of an attack on the craft, it could submerge and remain underwater for a period of up to five hours. Although this project was never proceeded with, it did bring Maunsell to the attention of the Admiralty and at the same time earned him the reputation of being an eccentric.
Following the submersible observation post, in May 1940 Maunsell then proposed reinforced concrete fortress which could be floated to its chosen position and sunk This he called the Marine Fort Number 3 and he suggested that twelve such units be built and positioned some 10 to 20 miles off the German occupied French and Belgian coasts . Their purpose being to forewarn the Admiralty of an intended invasion and observe the movement of aircraft and shipping.
These fortresses weighing 3,500 tons each, were mounted on twin pontoons measuring 160' x 30'and were visible approx 25' above high water mark when sunk in position. They were to be completely self sufficient with diesel generated electric power and heating and held a crew of twenty men. They were to cost ;£800,000 each at 1994prices and could be built within two months
Suggested armament for the 4ft thick reinforced pillbox was two heavy anti shipping guns and several anti aircraft Bofors guns, plus a searchlight. Once again the project was not proceeded with but it had obviously generated some ideas within the Admiralty .
In October 1940, following a request from the Admiralty, Maunsell designed yet another fortress which he called Marine Fort Number 4. Also known as the Thames Estuary Martello Towers, it was proposed to build three of these units and space them approximately 6 miles apart along an imaginary line drawn between Margate in Kent and Clacton on Sea in Essex.
These positions having been suggested by Commander Shankiand of the Port of London Authority, then in charge of the Thames Estuary. Once again the design employed a pontoon base,this time a single unit L80' long x 80' wide, weighing 2623 tons, on top of which was located a "citadel'' weighing 1,900 tons. This housed the gun platforms,magazines, engine room, stores and crew accomodation for 50 officers and men.Armament was to be two 6" guns, one Bofors anti aircraft gun and two searchlights. The cost of the three fortresses was estimated at £3,250,000 at 1994prices.
Building time was stated to be four months for the first fortress with further completions following at monthly intervals. In other words all three fortresses could have been built and placed in position within six months. No actual construction was undertaken on this design.Obviously, following the fall of France and the rest of Europe, and the threat of a German invasion imminent, the situation the Government was quite pressing.
Enemy E boats were attacking convoy shipping gathering in the Thames Estuary, enemy mines were being laid in the shipping channels and the German bombers attacking the London Docks had little trouble following the river to find their target.The Admiralty thus asked Maunsell yet again in November 1940 to prepare designs for building five fortresses based partly on the previous submissions, it utilised the twin pontoon idea, but with a revised top consisting of twin towers rising from the pontoons, upon which a gun platform was situated.
The twin towers held the engine room and crew accomodation for 100 men, as well as ammunition, stores and supplies to enable the fortress to be self sufficient for up to five weeks.With this proposal, Maunsell submitted the method of construction which in itselfwas quite unique and advanced for the time. Each fort was to be consist of fiveparts:-
1) The reinforced concrete pontoon or floats, there were two to each fort and each pontoon was 152 ft in length, 32 ft wide and 20 ft deep. The weight of each pontoon when complete was 817 tons.
2) The Pedestal, which consisted of a single reinforced concrete structure straddling the two pontoons, it was 8 ft high.
3) The Towers, of which there were two to each fort. They consisted of two drum like structures, each 24 ft in external diameter and Ift thick. The height of each tower was 60 ft, which was divided into five floors, each fitted out to be either living accomodation, workshops or stores.
4) The Deck, consisting of a reinforced concrete slab surrounded by a parapet and provided with adeck house.
5)The Equipment, comprising of two hoists, stairways, doors and partitions, cupboards, lockers, bunks, 25KW Diesel electric generating set, ventilating fans, pumps , sea cocks and bases to fix guns and searchlights.
The method of construction as laid down by Maunsell used three berths and was as follows:-Berth one was for building the pontoons. It consisted of a shallow basin or dry dock fitted out with removable timber gates at the riverside end. Berth two was used for the construction of the towers and superstructure and was tidal, It consisted of a level area which just dried out at low tide. Berth three was to be a deep water berth where the forts could be moored and remain afloat at all states of the tide during the fitting of equipment stage.
Work on the pontoons was to commence immediately following the preparation of
the site. Two pontoons were to be built simultaneously and therefore two sets of shuttering were required. Once the external wall shutters had been set up , the steel reinforcement for the floor was laid and approx 100 cu yds of concrete poured in one operation. The internal shutters for the sides of the pontoon, the bulkheads and the interior frames were then set up resting upon the floor concrete and at the same time the steelwork for the bulkheads was fixed.
The concrete in the sides, bulkheads and floor beams was then poured in one operation. All the internal shuttering was then stripped and steel posts bolted on to the floor beams. The deck reinforcement was placed in position and the deck concrete poured in one go. At this stage the pontoons could be floated out by removing the removable panels at the front of the cofferdam and allowing the water to rise inside the cofferdam.
The pontoons were then floated to berth two for the constsuction of the towers and
superstructure to begin. Meanwhile the panels were to be replaced in the cofferdam and work started on another two pontoons. The time estimated for the completion of the pontoon cycle was 29 days.
At berth two, previously prepared pedestal shuttering built in large sections was to
be placed in position and the reinforcement added. Concreting of the pedestal was to be one operation.
Tower base slabs, having been prepared previously, were then put in position and concreted., The tower sections, 20 ft high were then formed until the height of 60 ft was attained. The deck reinforcement and concrete when deposited, thus completed operations at berth two. The time estimated to construct the twin towers ready for the fitting out operation was 43 days. At Berth three, the fitting out and equipment installation took approximately 10 days.
Following the submission of the proposal, the Admiralty asked Maunsell in a letter dated March lOth 1941, to investigate the building of the Thames Estuary forts further. As a result, a recommendation that the Red Lion Wharf site at Northfleet be utilised was made, along with the suggestion that the civil engineering company, Holloway Brothers, then engaged locally at Dartford building the Littlebrook "A" power station, be nominated as the building contractor.
Maunsell again modified the design, this time settling on a single pontoon reinforced concrete base, 168 ft long, 88 ft wide and 14 ft deep, upon which twin 24 ft diameter towers, 60 ft high but with seven floors instead of five, were placed. On top of this was a gun deck,with two 3.7" guns ,officer's quarters and administration offices.
Above the offices were mounted two Bofors anti aircraft guns and on yet another floor, Radar and other "special" equipment. Using the procedure specified by Maunsell as detailed earlier, work commenced on the first pontoon in July 1941 under the supervision of the engineer in charge Mr John A Posford MICE. Work on the first Naval fort took a little longer than anticipated and completion was not until January 1942.
It was fitted out and commissioned on the 8th February 1942, H.M.Fort " Roughs Tower". It was towed to Tilbury for "Degaussing", which usually took 24 hours, prior to being towed down the river. Due to very bad weather conditions prevailing at the time, the fort was not towed down river to position 51.33.66N 1.28.93E and sunk until 1lth February 1942.
In order to familiarise the crews of the forts with their equipment and quarters, it was decided to install a full complement during the fitting out stage. Thus they became "au fait" with the running of the equipment from day one. When the fort was towed to her final position, the crew were on board manning the guns and ready for any enemy attack.
The method of sinking The forts was at the time another grey area because no one knew precisely what would happen when a 4,500 ton top heavy monster was suddenly flooded and allowed to sink. Although calculations had been made, it was a question of suck it and see. At this first sinking, after opening the flood gates, the fort took some 15 minutes before sinking by the bow and hitting the bottom.
It took a further one and a half minutes before the rest of the pontoon sank and the fort took an upright position During this period there were many frightened crew and onlookers who thought that the fort might tilt over sideways It was thought that the bow of the pontoon would be crushed by the speed of the descent and so for future sinkings it was decided to place a reinforced concrete buffer tube over the bow just prior to the sinking, to take the impact of the fort striking the bottom..