Vosper Ltd and John Thornycroft & Co Ltd were both ship builders building all sizes of vessels including fast patrol boats, in 1966 the companies merged to form the Vosper Thornycroft Group. Fast hovercraft seemed a natural step forward and in 1965 an application for a licence to produce hovercraft was made and a small hovercraft department (a small department, not small hovercraft) was formed within the group. The licence was obtained in late 1967 and the hovercraft department was expanded. The works was at Paulsgrove, within Portsmouth Harbour - see picture showing VT1-001 and VT1-002 (nearest camera) under construction.
Whether by intent or due to limitations in the original licence, VT used non-air propelled technology, this did have the advantages that water propellers were quieter and more efficient than air propellers and also that the 'sideways skid' typical of hovercraft when turning was reduced due to the keels (aka as skegs) in the water beneath the craft - however the major disadvantage was that the craft were not fully amphibious.
The VT1-M was the first craft produced by Vospers and was launched in 1968 (?). It was described as 'semi-amphibious' and was a 40% scaled model of the intended production craft - the VT1-M was a five ton manned craft used "to confirm the estimated and tank test performance". The description 'semi-amphibious' referred to the fact the craft could nose up onto a beach of suitable slope to allow passengers and vehicles to embark.
The full size VT1 craft were built at Portchester and the prototype (001) was launched on 29th August 1969. Two production models followed. The VT1 was never really accepted; apart from some trial routes used to evaluate it around the UK and Scandinavia, the VT1 never went into serious operation. The two production models were scrapped in Portsmouth harbour in 1973.
In 1972, Vosper Thornycroft decided to convert the prototype VT1 into a fully amphibious craft by removing the skegs and water screws and replacing them with two ducted fans at the back of the craft (they must have obtained a change to their original licence). After conversion, the craft was renamed as the VT2.
The VT2 was purchased by the UK MOD(N) for evaluation by the Navy and the Interservices Hovercraft Unit. No further orders were placed for the VT2.
Around 1981, following the closure of the Naval Hovercraft Trials Unit, the VT2 (together with several spare engines and other parts) was purchased by Hoverspeed as it had the same marinised Proteus engines used to power the SRN4s used across the English Channel. The VT2 was parked at Ramsgate (the Pegwell Bay hover terminal) whilst it was stripped and scrapped.
With the sale of the VT2 to Hoverspeed, the involvement of Vosper Thornycroft with hovercraft ceased, although the Vosper Group continued to be involved via their holding in Vosper Hovermarine.
If anyone knows the history of Vospers from 1972 to the end (or any part of it), please let me know because this is a missing piece of the story.
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