The occupation in the spring of 1940 crippled Britain's ability to gather intelligence information. After the Germans invaded Norway, many Norwegians knew that small boats were constantly sailing from the Shetland Islands to land weapons, supplies, and agents and to rescue refugees. In The Shetland Bus, David Howarth, who was second in command of the Shetland base, recounts the many, many trips made by fishing boats in the dark of Arctic winter to resist the Nazi onslaught.