Often engaged in hand to hand combat in beating down insurrection movements against Yet-sen. At all times wore a gun in his shoulder holster and one in a hip holster (thus earning the nickname "Two-Gun) and often led the charge into enemy lines. Devised methods of intelligence gathering, establishing sophisticated networks involving common farmers in various provinces of China as well as foreign diplomats and businessmen. Also, employed various levels of interrogation to extract information from captured enemies, including torture and execution.

After Yet-sun's death in 1925, Cohen assumed the same role with Chiang Kai-shek, Yet-sun's successor. Worked vigorously to gather information about the Chinese Communist Party which was gaining a foothold in China. Likewise, obtained information from people close to Japanese military intelligence. Learned that Japanese military intelligence officer Major Ryukichi Tanaka and his mistress Eastern Jewel planned to create a violent disturbance in Shanghai in order to provide Japan with an excuse to attack and invade the city. Warned Kai-shek, but was taken prisoner by the Japanese which in Hong Kong.

Was released by the Japanese after the end of World War II. Upon his return, found that he had been replaced in his position and left China. Eventually returned to Canada where he died in 1970.