Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. This was a great tool during the war. As it takes relatively long to send a message in morse code, transmitting stations, such as WWII clandestine agents, were prone to detection by means of Direction Finding. During WWII, both the Germans and the allies developed sophisticated methods for such Direction Finding (DF). Morse code can be a very hard to learn.