In anticipation of entering World War II, the United States War Department authorized four new aircraft assembly plants, including a Glenn L. Martin Company bomber plant built at Offutt Airfield near Bellevue, Nebraska. The Aircraft Manufacturing and Assembly Building, more commonly known as Building "D," but also as Facility 301, was the largest and most significant building within Martin complex. Industrialist architect Albert Kahn designed the enormous structure, which measured 900' long and 600' wide when completed in 1941. The lower and upper main level floors were concrete and covered with thousands of wood blocks dipped in creosote and oil and set on end for durability, safety, and comfort. Building "D" is considered to be one of the most historically significant World War II-era buildings in the United States.

The factory produced Martin B-26C Marauder medium bombers and Boeing B-29 Superfortress very heavy bombers under license. The facility was manufacturing more than fifty B-29s per month along a never-before-seen mechanized conveyor system by the end of 1944. The workers there also produced the first atomic bombers, Enola Gay and Bockscar.