During the initial phase of the War, he fought several battles, including the engagement at Surprise Hill ("Vaalkop") and in the Boer victory at Spionkop. After a string of Boer defeats in set-piece warfare and the British capture of Pretoria, Reitz was one of the fighters who remained in the field. He joined General Smuts who decided to conduct guerrilla operations, not in the territories of the Boer republics, but in the Cape Province. They faced immense difficulties, both from British forces and from nature, and when the majority did break through to the Cape they were on their last legs.