On 9 December 1899, De Wet received a telegram from the State President, M.T. Steyn, informing him that he had been appointed a fighting general and was to proceed to the Western frontier. He found General Piet Cronjé in command of the Boer forces ensconced at Magersfontein, south of Kimberley, while the English were at the Modder River. De Wet was to be Cronje's second-in-command. The British advance commenced on 11 February 1900, with General French outflanking Cronje at Magersfontein and riding towards Kimberley. De Wet's raid on the ox wagon convoy at Watervals Drift, capturing 1600 oxen, did not stem the tide. The Siege of Kimberley was relieved on 15 February, and Cronje surrendered with 4000 men at Paardeberg on 27 February. Shortly thereafter, de Wet was appointed Commander-in-Chief of the Free State forces. They could not contain the British advance towards the Free State capital, Bloemfontein, which was taken unopposed on 13 March 1900.