With the increased demand, and already overstretched with passenger routes from Lisbon to Angola and Mozambique, to the Portuguese State of India, Macau and East Timor, in 1940 "Companhia Colonial de Navegação" decided to purchase "Princess Olga" to carry greater numbers of passengers between Portugal and its colonies. Prior to this, the service had been carried out by pre-First World War liners, like "Colonial" and her sister ship "Mouzinho", the former SS "Corcovado". The "Princess Olga" was bought in April 1940, re-named "Serpa Pinto" and sailed to Lisbon. Her first voyage under the Portuguese flag was carried out soon after her arrival in Lisbon in May 1940, sailing to Lourenço Marques. When Italy declared war on the Allies in June 1940, all Italian shipping routes were closed. Only three companies from neutral countries maintained their transatlantic routes. These were the Portuguese "Companhia Nacional de Navegação" and "Companhia Colonial de Navegação" and the Spanish "Ybarra", from Seville. The Spanish company, however, did not have enough ships to best utilize the transatlantic routes. From August 1940 "Serpa Pinto" began her service on the transatlantic routes between Lisbon, and Rio de Janeiro and North America (Philadelphia and New York). She was repeatedly stopped in mid-Atlantic by German submarines and US Navy and Royal Navy ships for inspections. On 26 May 1944, on its way from Lisbon (departure 16 May 1944) to Port Richmond, Philadelphia, USA (arrival 30 May 1944), the "Serpa Pinto" was stopped in the mid-Atlantic by the German U-boat U-541. The U-boat's captain ordered the "Serpa Pinto"s crew and passengers to abandon the ship in the lifeboats, and requested permission from Kriegsmarine headquarters to torpedo the ship. The passengers and crew, with the exception of the captain who decided to remain on board whatever the German decision, duly left the ship in the lifeboats. There they were forced to wait all night while the German U-boat awaited a reply to its request. By dawn an answer had arrived from Admiral Karl Dönitz, who refused permission to sink the ship. The U-boat then departed the area and the lifeboats returned to the ship. The ship's doctor, a cooker and a 15 months child drowned during this incident.