<P> On the eve of World War II, the Union of South Africa found itself in a unique political and military quandary . While it was closely allied with Great Britain, being a co-equal Dominion under the 1931 Statute of 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 . </P> <P> 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 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, if not pro-Axis, led by Hertzog . </P> <P> On 4 September 1939, the United Party caucus refused to accept Hertzog's stance of neutrality in World War II and deposed him in favor of Smuts . Upon becoming Prime Minister, Smuts declared South Africa officially at war with Germany and the Axis . He immediately set about fortifying South Africa against any possible German sea invasion because of South Africa's global strategic importance controlling the long sea route around the Cape of Good Hope . </P> <P> John Vorster and other members of the pro-Nazi Ossewabrandwag strongly objected to South Africa's participation in World War II and actively carried out sabotage against Smuts' government . Smuts took severe action against the Ossewabrandwag movement and jailed its leaders, including Vorster, for the duration of the war . </P>

Who announced that south africa would join the war