The British patrol torpedo boats of the Vosper 70 class were authorized in 1938 and the first units were built in Vosper Portsmouth in 1939-40.
These were MTB (Motor Torpedo Boat) units of 70 feet in length, hence their denomination. A more advanced model of MTB equipped with heavier
armament was the Vosper 73, of which sixteen units were built in 1944. Both types were retired from service in 1945. The illustration depicts
a basic Vosper 70 model armed with two torpedo tubes and a twin 12.7-millimeter machine gun mounting.
Albeit in the First World War the Royal Navy had used numerous coastal boats Thornycroft CMB, the monetary difficulties and the absence of
tactical demands for fast torpedo boats had prevented subsequent developments until 1935, when it was ordered to the British Power
Boat Company the construction of prototypes of this genre; albeit they constituted the base of the British MGB (Motor Gun Boat) and the
American PT (Patrol Torpedo), the majority of British torpedo boats were built following projects from Vosper.
The primitive MGB was the result of the modification of the MA/SB (Motor Anti/Submarine Boat), to which heavy artillery was installed to
face the German S-Boats; however they lacked torpedo tubes. On the other hand the Fairmile Type D was a larger boat with the combined armament
of an MTB and an MGB; over 200 units were built from 1942. The size and armament of these models was increased along the war, and the last ones
had reinforced hull and radar. During the war 38 of these boats were lost and the rest were retired from service from 1945.
There were no British engines that were adequate for these boats so until Italy entered the war engines Isotta Fraschini were used. Eventually a
normalized engine Packard was installed when the problems with the transmission were solved. The gasoline engines made the British boats more
vulnerable to fires than the German counterparts, propelled by Diesel engines. A normalized hull was used for the majority of the boats built
during the war to allow the placement of disembarkment cables.
Vosper 70 class: 28 units (twelve with Isotta Fraschini engines)
Type: Patrol torpedo boat
Length: 21.4 meters
Beam: 4.5 meters
Draft (maximum): 1.5 meters
Displacement (standard): 40.4 tonnes
Propulsion: 3 x shaft, 3 x gasoline engine Isotta Fraschini/Hall Scott, 3600 horsepower
Speed: 42 knots (77.8 kilometers/hour) with Isotta Fraschini engines; 29 knots (53.7 kilometers/hour) with Hall Scott engines
Armament (typical): 2 x 533-millimeter torpedo tube, 2 x 12.7-millimeter machine gun, 2 x 7.7-millimeter machine gun, 4 x depth charge