The importance of reducing friction between an icebreaker's hull and the ice or snow by hull lubrication has been known for a long time and bow screws have been used on ships designed for sub-Arctic conditions. These propellers, however, are at high risk in Arctic conditions and this prompted intensive research in the 1960's at the Oy Wärtsilä Ab Helsinki shipyard to try to find an alternative method for use on icebreakers venturing further north. The idea of using air bubbles to create a lubricating water stream arose from the investigations of the two phase propulsion system, in which the propulsive effect is obtained by mixing gas and liquid, carried out at the Helsinki University of Technology. Model testing and detailed design of the system started immediately, and the first installation was made in 1969 in the roll on roll off ferry MS Finncarrier (Fig 1).