Mockup of the XM-2 "<a href="https://en.wikipedia.org/wiki/people_sniffer" class="extiw" title="en:people sniffer">people sniffer</a>" on a UH-1 aircraft
U.S. Army
<a rel="nofollow" class="external text" href="https://history.army.mil/html/books/090/90-21/CMH_Pub_90-21-1.pdf">VIETNAM STUDIES: Tactical and Materiel Innovations</a>, US Department of the Army. 2002. page 81