The Russian 450 and 600hp inland pusher tugs according to a CIA report dating from the 1950s

An item referred to the publication Susa Novykh Tipoc dlya Bol’shoy Volgi, written by A.P. Strakhov, Moscow 1954 dealing with new kind of ships to serve on the Volga. The river channel would in the future be changed caused by constructing of hydroelectric power projects and corresponding attendant reservoirs. So in this manner were new types of river ships needed. Except for the 150hp and 350hp pusher tugs were also a 450hp pusher tugs, fitted out with 303D^engines and a 600hp pusher tug designed, the latter fitted ouwt with 2x300hp 3D12 engines.

Source
The report was published on www.archive.org, document number CIA-RDP81-00280R000200210013-9