De Jong, Petrus Josef Sietse (pāˈtrüs yōˈzəf sēĕtˈsə də yông) [key], 1915–, Dutch naval officer and politician. Having entered the royal navy in 1931, he served as a submarine commander in World War II and rose in the navy after the war. He was state secretary for defense (1959–63) and then headed the ministry of defense (1963–67). A member of the Catholic party, he served (1967–71) as prime minister and minister of general affairs, ruling a coalition of Christian and conservative parties. He resigned when his coalition lost its ruling majority in general elections. Shortly afterward he was appointed a senator of the upper chamber of parliament.