Guillet's Eritrean troops paid a high price in terms of human losses, approximately 800 died in little more than two years and, in March 1941, his forces found themselves stranded outside the Italian lines. Guillet, faithful until death to the oath to the House of Savoy, began a private war against the Allies. Hiding his uniform near an Italian farm, he set the region on fire at night for almost eight months. He was one of the most famous Italian "guerrilla officers" in Eritrea and northern Ethiopia during the Italian guerrilla war against the Allies occupation of the Italian East Africa.