The 73ft High Speed Launches were the only HSLs to be built by the famous builder Vosper during WWII. In 1942 the RAF were looking for a suitable type of high speed launch to replace the then existing BPB 64ft and 63ft designs, both of which had a good speed, but were regarded as bad sea boats. The requirement was for a craft that was somewhat specialised, as it called for an HSL suitable for operation particularly in the Westertn Approaches with its hazardous winter weather conditions. Although the 67ft Thornycroft replaced the BPB types, in April 1942 two other types were chosen, both for their designed sea-keeping and endurance. One type was the 73ft Vosper High Speed Launch.
A shortage of suitable engines available meant that the Vosper design was powered by Thornycroft RY12 engines which resulted in a rather low speed of 25 knots. However one feature of the Vosper design was the engine layout, where two small engines wee able to drive the craft through a common drive box to extend the craft's range with main engines stopped. The designers had little time to complete the prototype to the required specification, hence the lines of the well proven Fairmile "D" were adopted, a good compromise between pure hard chine and round bilge designs. The Vosper 73ft HSL therefore was virtually a "short" Fairmile "D". The craft did tend to wallow around, however the important ability of the craft to head into sea at speed relatively smoothly was fully appreciated by the crews.
A total of 15 of the 73ft HSLs were ordered by the RAF, all entering service in 1943. This type of craft were operated almost exclusively from bases in Scotland, the Shetlands, the Hebrides and even further north in Iceland. Only one craft was lost during WWII, as a result of colliding with an aircraft whilst effecting a rescue.
Post war, the remaining craft were all transfered to the Admiralty for disposal in 1946, most ended up at Dumbarton and were disposed of through Marine Craft Constructors Ltd. None of this type are known to survive.
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