As a strategic and military outpost for the British, the sea lanes off the Straits of Malacca were important to be kept free from pirates and open for shipping. As the British expanded in influence and power, so Singapore stood in the gap between East and West interests as a natural deep-harbour destination that played host to the French, Portuguese, Dutch and other European navies and their men. Other seaports in Asia, from Shanghai to Calcutta, also played a role in the traffic of women and girls for prostitution.