This is one of the motor launches which operated out of Dover as part of No.52 ML flotilla, manned by the Royal Norwegian Navy. They operated at night during moonless periods in conjunction with the Royal Navy No.50 ML flotilla to lay mines in German convoy routes and to block enemy port entrances between Zeebrugge and Boulogne. Very dangerous work with the ever present threat of German E-boats. (See book entitled "Dover at War 1939-45" by Roy Humphreys).
One of the Motor Torpedo Boats (MTB's) which operated with the RN 11th MTB flotilla based at HMS Wasp in Dover, and manned by the Royal Norwegian Navy for a time at Felixstowe, has been preserved at IWM Duxford. The Coastal Forces Heritage Trust hope to move her to the Historic Naval Base collection at Portsmouth.
http://www.nationalhistoricships.org.uk/register/531/mtb-71
http://www.coastal-forces.org.uk/news.html 