Vosper was/is a British company. Off and On during the developement of OUR PT Boats..The British were influential. Apparently WE built some Vosper designed boats in this country using various American builders.
ALL the Vosper designed boats were intended for "Lend Lease". That meant WE GAVE the boats to foreign nations..including Russia... to use at their discretion. Near the end of the war..many contracts were cancelled. I have no idea what power these boats had originally.
I am still suspect of "Ride Boat" PT-728. You can Google it and get many hits...videos. You can decide.
NB