Petrus Jozef Sietse (Piet) de Jong (Apeldoorn, 3 April 1915 – The Hague, 27 July 2016) was a Dutch politician of Katholieke Volkspartij (KVP). From 5 April 1967 to 6 July 1971, he served as Prime Minister of the Netherlands. Previously, he was State Secretary for Defence (27 June 1959 – 24 July 1963) and Minister of Defence (24 July 1963 – 5 April 1967). Prior to his political career, he fought as a submarine commander in the Second World War.