Military history of South Africa during World War II September 1939, Britain declared war on Germany two days later. A short but furious debate unfolded in South Africa, especially in the halls of power in the Parliament of South Africa. It pitted those who sought to enter the war on Britain's side, led by Smuts, against those who wanted to keep South Africa neutral, led by Hertzog. On 4 September 1939, the United Party caucus refused to accept Hertzog's stance of neutrality in World War II and deposed him in favour of Smuts. Upon becoming Prime Minister, Smuts declared South Africa officially at war with Germany and the Axis.
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: