In 1623 and 1624, Lonck participated in the expedition of Admiral Willem de Zoete against the Barbary Coast pirates. Having made admiral by 1628, Lonck, in the service of the Dutch West Indies Company, joined Admiral Piet Hein in the Battle in the Bay of Matanzas, a naval battle during the Eighty Years' War in which a Dutch squadron was able to defeat and capture a Spanish treasure fleet.