War II. Hertzog resigned rather than accept the ruling and Smuts was elected in his stead. Upon becoming Prime Minister of South Africa, Smuts declared South Africa officially at war with Germany and the Axis. Smuts 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. Smuts took severe action against the pro-German South African Ossewabrandwag movement (they were caught committing acts of sabotage) and interned its leaders for the duration of the war. (One of them, John Vorster, was to become future Prime Minister of South Africa.) (See Jan Smuts during World War II.) Prime Minister and Field Marshal Smuts Prime Minister Jan Smuts was the only important non-British general whose advice was constantly sought by Britain's wartime Prime Minister Winston Churchill. Smuts was invited to the Imperial War Cabinet in 1939 as the most senior South African in favour of war. On 28 May 1941, Smuts was appointed a Field Marshal of the British Army, becoming the first South African to hold that rank. Ultimately, Smuts would pay a steep political price for his closeness to the British establishment, to the King, and to Churchill which had made Smuts very unpopular among the conservative nationalistic Afrikaners, leading to his eventual downfall, whereas most English-speaking whites and a minority of liberal Afrikaners in South Africa remained loyal to him. (See Jan Smuts during World War II.) Military contributions and casualties in World War II South Africa and its military forces contributed in many theatres of war. South Africa's contribution consisted mainly of supplying troops, men and material for the North African campaign (the Desert War) and the Italian Campaign as well as to Allied ships that docked at its crucial ports adjoining the Atlantic Ocean and Indian Ocean that converge at the tip of Southern Africa. Numerous volunteers also flew for the Royal Air Force. (See: South African Army in World War II; South African Air Force in World War II; South African Navy in World War II; South Africa's contribution in World War II.) The South African Army and Air Force helped defeat the Italian army of the Fascist Benito Mussolini that had invaded Abyssinia (now known as Ethiopia) in 1935. During the 1941 East African Campaign South African forces made important contribution to this early Allied victory.