Some tugboats serve as icebreakers or salvage boats. Many military and some civilian (such as some icebreakers) ships use nuclear marine propulsion. Besides its six nuclear icebreakers, Russia also has 19 diesel polar icebreakers. Prokhorov invested in an innovative Finnish freighter that did not require icebreakers. The Hope Icebreakers were a Canadian Junior ice hockey team. Both ships are planned to be replaced by three heavy and three medium icebreakers. Russia has eight nuclear icebreakers in service or building. Civilian "Arktika" nuclear-powered icebreakers are based at Murmansk. Russia currently operates all existing and functioning nuclear-powered icebreakers. Russia is the only country that currently has nuclear-powered civilian surface ships, mainly icebreakers. The only country constructing nuclear-powered icebreakers is Russia. Some shallow draught river icebreakers have been built with four propellers in the stern. It is home port to Atomflot, the world's only fleet of nuclear-powered icebreakers. The U.S. Coast Guard icebreakers and also sailed in support of the expedition. Russia started building new icebreakers, Project 22220, in 2013.