My uncle told me that just before we had war with Japan. Japanese government sent some officers to China and they all dressed like monks. Of course, people didn't suspected these "monks". These "monks" walked around cities and talked to people (yes, these monks knew how to speak Cantonese and Mandarin). After war broke out, the Chinese government wondered why Janpanes soliders knew some big cities surroundings better than Chinese soliders. After some people recongized some officers were the "monks", the Chinese government found out what the "monks" did - drew maps of big cities.
日本人擅闯军事区被捕 日称搞建筑的