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Swimming Shermans DD's

Discussion in 'Allied Motorised Weapons' started by Jim, Sep 14, 2007.

  1. Jim

    Jim Active Member

    Sep 1, 2006
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    Nicholas Straussler
    Born in 1891, Nicholas Straussler Settled in Britain shortly before the Second World War. He already enjoyed a reputation as an innovative automotive engineer in his native Hungary, but by forming links with firms such as Alvis Ltd in Coventry and the armaments manufacturer Vickers he found more potential business in Britain. For the former he designed a range of armoured cars and for the latter, in the main various attachments and accessories for tanks. Straussler's innovative streak could get out of hand, particularly with automotive projects that were not always practical. When it came to amphibious tanks, however, he could at least see the wood for the trees.
    In a note written in 1945 Straussler claims that after examining- various types of buoyant tanks he reached the conclusion that it made more sense to apply flotation equipment to standard designs. Thus, in cooperation with Vickers-Armstrong he developed a range of collapsible floats that could be used to create pontoon bridges and rafts or, attached to each side of a light tank, to keep it afloat. The War Office was sufficiently interested to test this equipment and various light tanks were modified for trials, sometimes with the addition of an outboard motor. They appear to have worked well enough, but Straussler had visions of invasion beaches cluttered up with discarded floats after a landing, and duly turned his attention elsewhere.
    One has to be cautious when dealing with recollections, particularly when the subject was amassing evidence for a Royal Commission that might result in a substantial reward, and Straussler's suggestion that he realized the limitations of his floats and cast about for an alternative as early as 1934 does seem a bit surprising. If true he was way ahead of the War Office, who persisted with the float idea well into the Second World War.

    The prototype
    Whenever it did occur to him, Straussler's idea was a stroke of genius. It was simple enough in theory since it relied upon displacement; the clever bit was Straussler's method of achieving it. In order to avoid the bulk normally associated with displacement he surrounded the tank with a collapsible, waterproof screen. This in turn was attached to the tank's hull, just above track level and the joint securely sealed, with the result that the upper half of the tank and its turret, although essentially below water level, remained dry while the lower half, including the tracks and running gear, was immersed. For trial purposes Strausler was given a redundant Tetrarch, or Light Tank Mark VII, from the 1st Armoured Division which thus became the first Duple Drive (DD) tank, and this is the odd thing. Anyone looking at the tank, in its amphibious guise, would be struck immediately by the canvas screen that effectively enclosed the upper part of it. This screen, with a slightly pointed bow and rounded stern end, was kept in shape at the top by a tubular rail but was raised and held upright by a series of rubber tubes, inflated with compressed air and held that way while the tank was afloat. Yet this strange screen and its amphibious capability formed no part of the tanks title. Duplex Drive simply indicated that it had two methods of propulsion: tracks on land of course but in the water a marine propeller.

    The prototype Tetrarch DD.


    A casual glance suggests that some sort of outboard motor was fitted to the Tetrarch, but upon closer inspection it is more like a marine inboard/outboard, probably designed especially for the tank. The three blade propeller, which faces forwards, is suspended below a gearbox arrangement from which a splined shaft extends into a tube at the rear of the tank that i driven from the tank's gearbox. When the Tetrarch is on dry land this drive is disengaged and the outboard part held at an angle, but for entering the water it is swung into an upright position when the two drive components meet. A flexible shaft, running from the top of the outboard to a position on the right side of the turret, controls steering, pivoting the outboard's lower section with a screw handle. The little tank took its first official dip in Hendon Reservoir in London in June 1941. General Sir Alan Brooke witnessed the display, and soon gave the go ahead for further development. Later the tank went to Portsmouth and did some saltwater flotation trials from the beach at Hayling Island, but it can only have been suitable for calm sea condition. The screen itself was waterproof enough, being made from a rubberized canvas fabric produced by the P.B. Cow company makers of the Lilo inflatable air bed. Even so it did not offer very much freeboard and was probably not sufficiently rigid to hold up in rough conditions.
  2. Cabel1960

    Cabel1960 recruit

    Nov 4, 2006
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    I guess at the time on paper this invention was well before its time, maybe the casulties prove this but what a great invention been able to send tanks to the beach via the sea. Should i have been there to witness this from the German side i would have probably not beleived what i saw, imagine something in the shape of a tank swimming towards you, not only that when it reaches the beach it lifts its skirt to show it is a tank.. :eyes:

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