Esperanto was once used in the US army to realistically simulate the language situation when training. Has any nation ever employed other constructed languages in the military as code talkers?
From Wikipedia article:
Code talkers are people in the 20th century who used obscure languages as a means of secret communication during wartime. The term is now usually associated with the United States service members during the world wars who used their knowledge of Native American languages as a basis to transmit coded messages. In particular, there were approximately 400–500 Native Americans in the United States Marine Corps whose primary job was the transmission of secret tactical messages. Code talkers transmitted these messages over military telephone or radio communications nets using formal or informally developed codes built upon their native languages. Their service improved the speed of encryption of communications at both ends in front line operations during World War II.