Developed by The British Special Operations Branch for Commando and Special Operations use during World War II, The Welfreighter was a dual purpose vessel. It could serve as a ''fast boat'' during daylight operations and could be partially submerged at night time or for various covert operations. Classed as a Midget Submarine, The Welfreighter was nearly 40-feet in length and were constructed of light steel and wood. In daytime appearance, The vessel featured twin ''dummy masts'' which gave it the overall look of a small fishing ship. These masts were in reality communications and periscope poles for both day and submerged operations.
The Welfreighter used twin diesel engines capable of 44-HP each. The vessel could achieve 5-knots underwater and 7 on the surface. The Welfreighter was rated to 130-feet of depth. The vessel had a 1,000-mile operational range. Crewed by (2), The Welfreighter could transport up to 7 Commandos or special operatives and up to 2-tons of equipment. The Mark III version was only deployed once. Launched in early 1944, it supported Greek Partisans against Germany. With The War winding down no further needs for covert operations were seen as practical. The program was decommissioned with only (2) being produced.