 Despite U-boat operations in the region (centred in the Atlantic Narrows between Brazil and West Africa) beginning autumn 1940, only in the following year did these start to raise serious concern in Washington.This perceived threat caused the US to decide that the introduction of US forces along Brazil's coast would be valuable.After negotiations with Brazilian Foreign Minister Osvaldo Aranha (on behalf of dictator Getúlio Vargas), these were introduced in second half of 1941.