A drawing of the Martin Commercial Transport, an airliner variant of the Martin MB-1 bomber.
Unknown author<span style="display: none;">Unknown author</span>
<i>Flight</i>, 13 January 1921, <a rel="nofollow" class="external text" href="https://www.flightglobal.com/pdfarchive/view/1921/1921%20-%200027.html?search=Martin%20Commercial%20Transport">page 27</a>