Comparing the cost of the B-29 and Manhattan Project

What was the most expensive weapons program of the Second World War?

The B-29 when programs are counted separately. The combined atomic-bomb and delivery-aircraft effort is larger when B-29 and specialist Lancaster work are counted with Manhattan.

The ranking depends on whether the nuclear weapon and its delivery aircraft are counted together. The B-29 is identified as the costliest separate program. Combining the Manhattan Project with the B-29 program and specialist Lancaster delivery work produces the larger total in this comparison. Some British project costs are also described as difficult to compare because spending was spread across many years.