David Abbot’s 'Dark Albion — A Requiem for the English' page 21.The Empire Windrush was built in Nazi German as a troop carrier. Initially named the Monte Rosa, it was launched in 1930 as a cruise ship, and became the favorite cruise ship of top Nazi officials. When the war began she was first used as a barracks ship, and then as a troop carrier for the invasion of Norway. Stationed in Norway, she became an accommodation ship attached to the Tirpitz.
At the end of the war, as the Germans fled the Red Army, she was used as an evacuation ship. In May 1945 she was seized by the Allies and handed over to the British Ministry of Transport. Two years later she was renamed the Empire Windrush and, run by the New Zealand Shipping Company on behalf of the British government, was put to service carrying troops between Southhampton, Gibraltar, Suez, Aden, Colombe, Singapore and Hong Kong. Over the years in which she ran this route, extended during the Korean War to Japan, in 1948 she made one other journey — from Australia to Britain, via Kingston, Jamaica, where the emigrants, enticed by a newspaper advertisement offering on-way berths to Britain for £28 10s each, embarked.
Three years after the defeat of Hitler, she ship that heralded an ineradicable change in the complexion of Britain was a Nazi troop carrier.
BBC - Windrush, Who Exactly was on board?