Military history of South Africa during World War II Westminster with its head of state being the British king, the South African Prime Minister on 1 September 1939 was J.B.M. Hertzog – the leader of the pro-Afrikaner and anti-British National Party. The National Party had joined in a unity government with the pro-British South African Party of Jan Smuts in 1934 as the United Party. Hertzog's problem was that South Africa was constitutionally obligated to support Great Britain against Nazi Germany. The Polish-British Common Defence Pact obligated Britain, and in turn its dominions, to help Poland if attacked by the Nazis. When Adolf Hitler's forces attacked Poland on 1
Prime Minister of Australia becomes acting Prime Minister in those circumstances. Three Prime Ministers have died in office – Joseph Lyons (1939), John Curtin (1945) and Harold Holt (1967). In each of these cases, the Deputy Prime Minister (an unofficial office at the time) became an interim Prime Minister, pending an election of a new leader of the government party. In none of these cases was the interim Prime Minister successful at the subsequent election. As of , there are seven living former Australian Prime Ministers. The greatest number of living former Prime Ministers at any one time was eight. This has occurred twice: