The Soviet Navy never lost faith in the SSK, and continued to build them in parallel with SSNs. When the huge Project 613 ‘Whiskey’ programme came to an end in 1958 no fewer than 215 had been built, and 21 more were assembled in Chinese yards. The improved Project 633 ‘Romeo’ type never achieved the same popularity – 20 being built in 1956-64 for the Soviet Navy and others built for export. The Project 611 ‘Zulu’ type, a 1930.5-tonne (1900-ton) ocean-going boat, ran to 30 units, but large-scale production returned with the 62 Project 641 ‘Foxtrots’ built from the early 1960s to 1971. The 19 Project 641 BUKI ‘Som’ class (’Tango’) were specialised antisubmarine boats built from ‘Foxtrot’ components.
For details on the capability of the Romeo class diesels see A. S. Pavlov, Warships of the USSR and Russia 1945-1995, translated by Gregory Tokar. Annapolis, Md.: Naval Institute Press, 1997, p. 70. Very much like the battery capability given to the Tang class by the Americans to achieve the kind of speed displayed by the German Type XXI’s at the end of World War II, this boat had an increased number of batteries that provided the capability of remaining submerged for 300 hours at very slow speed. The Romeo also had hovering capability. In many ways, it was the ideal pre-nuclear surveillance boat. These vessels came off the ways in the late 1950s, roughly the same time as the advent of the first Soviet Nuclear boats, the November class.
