It is indeed the XB-19, later labeled the XB-19A when the radial engines were replaced. Until the B-36 came along it was the largest airplane ever made in the US. The Wikipedia entry is somewhat sparse, so here's a link to an excellent piece with some good photographs and links to further sources. This source says the XB-19A was in fact used as a transport; the Wikipedia piece gives the impression that using it as a transport may not have actually occurred.
https://foxtrotalpha.jalopnik.com/am...oug-1632864365