Gubbins argued that for guerrilla warfare to succeed it needed daring leadership and a sympathetic population. In his pamphlets he provided practical information on how to organize a road ambush, how to immobilize a railway engine and how to kill the enemy. By the outbreak of the Second World War Gubbins had reached the rank of brigadier. He joined the Special Operations Executive (SOE) and in November 1940 was appointed director of operations and training.