The only change was the installation of guns concealed below deck. To escape the notice of German patrols, the Shetland-Bus boats had to look like fishing boats. This meant that for several months in the summer the bus was idle as there were only a few hours of darkness in this northern area. The missions to Norway had to be carried out in darkness. After the initial success in the winter of 1940-1, the group was formally established. These organizations initiated a project using Norwegian fishing boats that had escaped Norway: to take agents across the North Sea to Norway and bring agents and refugees back. It was a project of both the Secret Intelligence Service (SIS) and the Special Operations Executive (SOE). The idea of the Shetland bus originated when a marine base was being established in late 1940 at Lerwick.

These three military vessels completed 116 missions without any fatalities. So in the fall of 1943 three American sub chasers were brought in to replace them. However, too many of the vulnerable vessels were being lost. Fishing vessels were used until the spring of 1943. The Shetland Bus ran 210 missions from August 1941 to the end of the war. This lifeline was maintained initially by a few Norwegian fishing vessels and later by American submarine chasers based in the Shetland Islands. It was risky and very dangerous, but it provided secret agents, radios, information and weapons while also enabling some of its endangered citizens to escape. During the German occupation during World War 2, Norway had a lifeline to the Allies across the North Sea.

The Shetland Bus by David Howarth