08/31/2010. Remarks by Johan Visschedijk: "Despite the heavy cancellations of B-29 orders at the end of World War II, plans already made for an improved version were enabled to continue. The improved model was originally to have materialized as the
B-29D, built of a stronger and lighter aluminum alloy and powered by the 3,500 hp Pratt & Whitney R-436O Wasp Major engine, a 28-cylinder four-row air-cooled radial engine.

A B-29A-5-BN was allocated to the engine manufacturer for the development, the complete installation, and the flight testing of the new power plant in a redesigned nacelle, being redesignated XB-44 after completion. Initial orders for the improved B-29 were cancelled, but were later reinstated as B-50A."