[vanir]

Nuclear carrying B-29's were known as the "silverplate modification" and it was in fact a series production of something like 36 planes. All weapons and armour was removed and substantial modifications were made to the bomb bay areas (fuel tanks added to the aft bay), mostly to accommodate the Fat Man style bomb, since the revised Little Boy style weapon could be accommodated in the standard B-29 bomb bay. A new crew station was placed in the cockpit to monitor the weapon and drop procedure. A new variant of the Wright R-3350 engine was fitted and reversable pitch propellers were included. Apparently these "silverplate" B-29's had vastly superior performance to the standard model.

Visually the obvious difference is no weapons or turrets. There is a long range reconnaissance variant of the B-29 which this looked identical to. Some USAAF heavy bomber/reconnaissance groups made a habit of overflying Japan in small numbers or as lone aircraft in the weeks leading up to the bombings.