The 30th Armoured Brigade commanded by Brigadier Nigel Duncan and was equipped with crab flails. Its three regiments were the 22nd Dragoons, the 1st Lothian and Border Horse and the 2nd County of London Yeomanry (Westminster Dragoons). Each of the brigade's Crab regiments was subdivided in a headquarters and three squadrons each of which had three troops of five Crabs. When engaged in line clearing three crabs of a troop advanced in formation over a 24 foot (7.30m) wide front, while the other two tanks remained in reserve to provide covering fire for the three actually mine-clearing. To enable the drivers of the Crabs to maintain formation, posts with lamps on them were fitted to the rear of the tanks. When not in use the posts could be unshipped and stowed in a special locker. The 1st Assault Brigade RE was under the orders of Brigadier G.L. Watkinson was equipped with AVRE's and also fielded three regiments - the 5th, 6th and 42nd Assault Regiments. RE. The 1st Tank Brigade was composed of the 11th Royal Tanks Regt., the 42nd RTR (23rd London Regt.) and the 49th RTR. The brigade was equipped with CDL's. However, Gen. Hobart's division was not engaged as a single bloc with its specialist material, but was spread out among the three assault divisions. Thus the 3rd.Division on Sword Beach was supported by the Crabs of A Squadron of the 22nd Dragoons and the AVRE's of the 77th and 79th Squadrons of the 5th Assault Regt RE. The 3rd Canadian Division on Juno Beach had the support of the Crabs of B Squadron of the 22nd Dragoons and the AVRE's of the 25th and 80th Squadrons of the 5th Assault Regt. RE. The 50th Northumberland Div. was supported on Gold Beach by the Crabs of Band C Squadrons of the Westminster Dragoons and the AVRE's of the 81st and 82nd Squadrons of the 6th Assault Regt. RE. The special armour was to precede the assault waves of the infantry coming ashore to dispose of the obstacles placed by the Germans enjoying the element of surprise over the defenders. These were some of the tasks assigned to them: Crossing anti-tank walls and ditches by placing SBG's or breaching them with the flying dustbin bombs. The latter were also responsible for dealing with the defenders' guns and bunkers. Charges were placed by hand by AVRE crews who dismounted. Ditches and bomb craters were filled with fascines and bridged over by SBG's. Steel beach obstacles were knocked over by the flying dustbins, gunfire from the Crabs or pushed aside by the bulldozers. The Crabs exploded the mines or the Bullhorn ploughs dug them up. The AVRE's fitted with bobbins unrolled their flexible carpets over the patches of soft clay. Once on shore the DD's were used as conventional tanks. The amphibious tanks was a part of the specialist vehicles trained by the 79th Armoured Div., but for D-Day they did not belong to the division.
The Sherman DD Tank A tank that could float and advance through water would at first appear to be an absurd idea but Nicolas Strausler solved the problem. A Hungarian by birth but naturalised British he was the originator of a number of inventions for the British Army including an armoured 4 x 4 before the war and a pliable boat among others. In 1940 to submitted his project for an amphibious tank to the War Office. Tests had already taken place with pontoons fixed to each side and with large air bags, but Strausler proposed a simple method of turning a tank into a veritable boat. A skirt of waterproof cloth formed an air pocket which allowed the monster to float. The first trials with a Tetrarch tank took place in June 1941 in a reservoir at Hendon, and Sir Alan Brooke, the GIGS, ordered immediate construction of these Duplex Drive (DD) tanks. DD Tank just been launched heading for landing beach. The Valentine tank was initially chosen and 600 of them were converted, but starting in 1942 the Sherman's started to arrive in quantity from America. It was also scheduled for conversion but proved initially too heavy and the system needed to be reinforced. The conversions were issued to the 79th Armoured Division. This special tank was fitted with decking over the entire hull and which came to a point. A waterproof cloth skirt was fixed to the deck which could be kept upright by means of 36 rubber tubes filled with compressed air and kept its shape by means of a metal framework. The skirt could be erected in fifteen minutes by an experienced crew, but on the other hand, the crew did not need to emerge from the tank to lower it which could be done rapidly which was essential as the tank had to able to fire as soon as it touched down on the shore. Sherman DD (Duplex Drive) amphibious tank with waterproof float screens. When in the water the float screen was raised and the rear propellers came into operation. 1944. The device was driven by two propellers and could manage a speed of 4 to 5 knots at sea. DD's could also be landed directly onto the beach from LST's and LCT's whereby they could intervene directly with their guns which gave them a great advantage. The Americans rejected the "funnies" with disdain which was to cost them dearly on Omaha as AVRE's would have enabled them to get off the beach far more quickly. DD's on the other hand were adopted widely by both armies. On D-Day the German defenders had the surprise of their lives when tanks came trundling out of the sea. Hitler has announced special weapons but it was the Allies who brought their special weapons out from the sea!
Although Duplex Drive allowed the landing craft to release the tank farther from shore, the alternative deep wading gear allowed a tank to drive partially or wholly underwater on the sea floor rather than swim. Deep wading Churchill's took part in the 1942 Dieppe raid and deep wading tanks operated on D-Day also. Allied tanks were given waterproofed hulls and air intake and exhaust trunking to allow them to come ashore from shallow water. Tall ducts extended from the engine deck to above the turret top and these needed to stay above water. The front duct was the air intake for the engine and the rear duct vented the exhaust. This device saw use in many amphibious invasions, and was used on light tanks and tank destroyers as well. The US had similar devices for trucks and jeeps. The Tauchpanzer III During the planning of Operation Sealion the Germans also developed tanks with the same purpose as the Sherman DD; to provide armoured protection to infantry during an amphibious assault. The Tauchpanzer III was a modified version of the Panzer III and, like the Sherman DD, was dropped from a landing craft around a mile off-shore. However, instead of floating the Tauchpanzer III drove on the sea-bed. A rubber hose supplied the engine and crew with air and gave the waterproofed tank a maximum diving depth of 15 metres (50 feet.) making it an extreme example of a wading tank. Many modern vehicles use similar devices