was postponed until 1925. South West Africa German South West Africa campaign, 1914–1915 An invasion of German South West Africa from the south failed at the Battle of Sandfontein (25 September 1914), close to the border with the Cape Colony. German fusiliers inflicted a serious defeat on the British troops and the survivors returned to British territory. The Germans began an invasion of the Union of South Africa to forestall another invasion attempt and the Battle of Kakamas took place on 4 February 1915, between the South African Union Defence Force and German Schutztruppe, a skirmish for control of two river fords over the Orange River. The South Africans prevented the Germans from gaining control of the fords and crossing the river. By February 1915, the South Africans were ready to occupy German territory. South African Prime Minister Louis Botha put Jan Smuts in command of the southern forces while he commanded the northern forces. Botha arrived at Swakopmund on 11 February and continued to build up his invasion force at Walfish Bay (or Walvis Bay), a South African enclave about halfway along the coast of German South West Africa. In March Botha began an advance from Swakopmund along the Swakop valley with its railway line and captured Otjimbingwe, Karibib, Friedrichsfelde, Wilhelmsthal and Okahandja and then entered Windhuk on 5 May 1915. The Germans offered surrender terms, which were rejected by Botha and the war continued. On 12 May Botha declared martial law and divided his forces into four contingents, which cut off German forces in the interior from the coastal regions of Kunene and Kaokoveld and fanned out into the north-east. Lukin went along the railway line from Swakopmund to Tsumeb. The other two columns rapidly advanced on the right flank, Myburgh to Otavi junction and Manie Botha to Tsumeb and the terminus of the railway. German forces in the north-west fought the Battle of Otavi on 1 July but were defeated and surrendered at Khorab on 9 July 1915. In the south, Smuts landed at the South West African naval base at Luderitzbucht, then advanced inland and captured Keetmanshoop on 20 May. The South Africans linked with two columns which had advanced over the border from South Africa. Smuts advanced north along the railway line to Berseba and on 26 May, after two days' fighting captured Gibeon. The Germans in the south were forced to retreat northwards towards