Front view of the experimental Lockheed XH-51A, circa in 1965.
U.S. Department of Defense
<a rel="nofollow" class="external text" href="http://www.navy.mil/ah_online/department_arch.html">U.S. Navy All Hands magazine</a> <a rel="nofollow" class="external text" href="http://www.navy.mil/ah_online/archpdf/ah196503.pdf">March 1965</a>, p. 43.