My Reminiscences of East Africa

Paul Emil von Lettow-Vorbeck (20 March 1870 – 9 March 1964) was a general in the Imperial German Army and the commander of its forces in the German East Africa campaign. For four years, with a force that never exceeded about 14,000 (3,000 Germans and 11,000 Africans), he held in check a much larger force of 300,000 British, Belgian, and Portuguese troops. Essentially undefeated in the field, von Lettow-Vorbeck was the only German commander to successfully invade imperial British soil during World War I. His exploits in the campaign have come down "as the greatest single guerrilla operation in history, and the most successful."

[Source: Wikipedia]