The OK-650 reactor is the nuclear fission reactor used singly to power the Soviet Navy's Project 685 Плавник (Mike), Project 971 Щука-Б (Akula), and Project 945 Барракуда, Кондор, and Марс (Sierra) submarines, and in pairs to power the Project 941 Акула (Typhoon) and Project 949 Гранит and Антей (Oscar) third generation submarines. It is a pressurized water reactor (PWR), using 20-45% enriched uranium-235 fuel to produce 190 MW of power. It also powers the new Project 955 Borei submarines