This article describes the conquest and occupation of German held South West Africa, now called Namibia, by forces from the Union of South Africa acting on behalf of the British Imperial Government at the start of World War I.

The outbreak of hostilities in Europe in August 1914 had long been anticipated and Government of the Union of South Africa were well aware of the significance of their common border with the German Protectorate of South West Africa. General Louis Botha, the leader of the South African Government, immediately offered to invade German South West Africa and the British government accepted his offer.

Early in September, 1914 South African troops were mobilized along the border between the two countries under the command of General Lukin and Lt Col Maritz. Shortly afterwards another force occupied the German port of Luderitz.

At this point Botha's plans went seriously astray; there was considerable sympathy among the Boer population of South Africa for the German cause; it was after all, only eleven years since the Boer War. The commandant general of the Union forces and many of his officers including Lt Col Maritz revolted against the government. Very quickly there were some 12,000 rebels under arms in the Transvaal and Orange Free State and they had to be subdued before continuing with the real war. This meant a delay of four months while the rebellion was suppressed.

Botha himself commanded the force that occupied Walvis Bay and Swakopmund in the north of the territory. In March, 1915, the South Africans were ready and moving in four columns they began the complete occupation of the German territory. The capital, Windhoek, was occupied on May 12 by which time the South Africans had taken over most of the country. An attempt was made to persuade the Germans to surrender at this stage but it was unsuccessful and the campaign continued with the German forces gradually being squeezed into the North West corner of the territory. They were defeated at Otavi on July 1 and surrendered on 9 July, 1915.

Maritz and the other rebels got off lightly being released from prison after two years, Botha recognizing the value of conciliation.