The designation B-29K had originally been assigned to the hose tanker
conversions of the B-29 that were eventually produced as KB-29M.
Since none of the tankers ever actually used the K suffix, it was
reassigned to a single B-29-BW that was used as a cargo transport and
Warbird History--B-29 Superfortress, Chester Marshall, Motorbooks
The Boeing B-29 Superfortress, Mich Mayborn, Aircraft in Profile,
B-29 Superfortress, John Pimlott, Gallery Books, 1980.
Boeing Aircraft Since 1916, Peter M. Bowers, Naval Institute Press,