<a href="https://en.wikipedia.org/wiki/Boeing_YB-9" class="extiw" title="w:Boeing YB-9">Boeing Y1B-9</a> with <a href="https://en.wikipedia.org/wiki/Curtiss_V-1570" class="extiw" title="w:Curtiss V-1570">Curtiss V-1570 Conqueror</a> liquid-cooled V12 engines.
U.S. Air Force
early 1930s <div style="display: none;">date QS:P,+1930-00-00T00:00:00Z/8,P4241,Q40719727</div>
<a rel="nofollow" class="external free" href="https://media.defense.gov/2006/May/11/2000557342/-1/-1/0/060421-F-1234P-039.JPG">https://media.defense.gov/2006/May/11/2000557342/-1/-1/0/060421-F-1234P-039.JPG</a> at <a rel="nofollow" class="external text" href="https://www.nationalmuseum.af.mil/Upcoming/Photos/igphoto/2000557342/">gallery page</a>