Production miracles built the American Air Armada in World War II

The miracle of production capacity that saw the United States build about 35,000 four-engine bombers during World War II, along with 50,000 fighters and thousands of medium bombers, transports and trainers, was a juggernaut with many moving parts.

In the first full year of American participation in the war, military and industrial planners faced demands on a scale never before contemplated. 

For key strategic bombers, multiple assembly lines were required to meet the need. Suppliers poured a steady stream of parts and subassemblies into the mix, with railroads and trucks carrying vital pieces to the prime contractors’ assembly lines around the U.S.

Air Force statisticians and historians captured numbers that paint a picture of a monumental wartime effort. Including the lead-up to war beginning in the last half of 1940 and concluding at the end of August 1945, American industry built nearly 300,000 military aircraft, supported by production of more than 800,000 engines and more than 800,000 propellers. The combined weight of all the airframes and spare parts was calculated at more than 2.8 billion pounds. All that tonnage came at a price approaching $45 billion, nearly one-fourth of the total American munitions program.

During 1940 as American manufacturers realized the first glimpses of increased production orders for military aircraft, only about 6,000 military airplanes were built, along with perhaps 7,000 civilian aircraft. By 1944, with wartime production at peak levels, more than 96,000 military aircraft were built, generally more complicated and larger than those of 1940.

Early in the war, the creation of new combat units absorbed as many aircraft as could be rolled out into the sunshine. All too soon, it also became necessary to produce aircraft to replace those lost in combat and accidents.

The global nature of the conflict and the evolving tactics of friend and foe demanded a continual evolution of aircraft designs and equipment, sometimes tailored to the needs of specific combat theaters.

It soon became apparent that it was impractical to introduce the latest changes, especially those tailored for only some theaters, on the assembly line. This would slow production. A network of pools for new aircraft and modification centers was set up in the United States to allow a semi-frozen design to be produced en masse, and tweaked at a separate facility with the necessary upgrades until those changes could be introduced on the production line without halting work.

A key example of this is the tail gun emplacement on the Boeing B-17G Flying Fortress. The first G-models used the same tail gun setup that had been introduced on the B-17E back in 1941. That was another epoch earlier compared to the war being fought by the B-17G in 1944. A new tail gun station that provided a larger cone of fire and better visibility for the gunner was devised, but initially G-models flew away from the Seattle plant with the outdated gun emplacement as an economy of time. These brand new B-17Gs arrived at a modification center operated by United Airlines in Cheyenne, Wyoming, where the old tail cap came off and the new version was attached before sending the bombers off to Europe for combat. The United facility performed other upgrades, saving time in the overall production of B-17s.

Even so, B-17s destined for the Eighth Air Force in England received the attention of thousands of mechanics who made sure they were up to date before entering combat, further streamlining the stateside production flow.

In the Pacific, B-25 Mitchell bombers received modifications in the field to render them more useful as strafers for low-level attacks. This post-production tinkering may have been fostered by the Fifth Air Force commander, General George Kenney, an engineer by background.

The B-24, a globetrotting bomber built in greater numbers than any other American warplane, was serviced by seven modification centers around the United States before heading overseas. Later in the war as modification centers emphasized completing B-29 Superfortresses, B-24s were parked in pools around the country awaiting modification line space. By January 1945 more than 900 new B-24s awaited mods; by VJ-Day more than 400 new B-24s were in stateside storage locations, according to Liberator historian Allan G. Blue.

When the Ford Motor Company became part of the military aircraft construction pool, Ford engineers hoped their years of experience in automobile mass production would serve the company’s aviation interests as well. But initially, the auto making giant faced some hurdles unique to the construction of aluminum aircraft instead of steel automobiles. When Ford commenced construction of B-24 Liberators as an adjunct to Convair, Convair engineers had to step in quickly to advise their Ford counterparts that, unlike car fenders, the holes drilled in aluminum aircraft parts could not be oversized or elongated to enable hand-fitting.  

But the Ford B-24 plant introduced other automated devices that accelerated production later. Ford became so proficient at building Liberators that by 1945, the five assembly lines building B-24s had been reduced to only two — the Convair home plant in San Diego and Ford at Willow Run, Michigan.

Aircraft manufacturers ramped up their mass production techniques in advance of American entry into the war. This enabled the task of building aircraft to be accomplished by workers including those of limited previous skills. This was a crucial advantage as the wartime draft claimed so many young men. Older men and women and those deemed unsuitable for military service gained employment in aircraft plants where their work did much to win the war. 

When aircraft manufacturers complained about losing skilled technicians to the draft, the Army Air Forces secured deferments for many. (My father, Carl Johnsen, told a story about being on a bus destined for an induction center when a man with a clipboard entered the bus, calling out for Carl Johnsen, and said he was needed at Northrop instead and should return to his job. We’ll never know how much of a factor in his selection was his age – he was 29 when Pearl Harbor was attacked – but Dad’s contribution to the war effort was drafting at Northrop, the start of an aerospace career that spanned four decades.)

The manufacturers wrestled with initial shortages of machine tools and a lingering concern over aluminum scarcity even as they increased the tempo of aircraft delivery. At the peak of production in 1944, 16 B-17G Flying Fortresses were completed during each one-day 20-hour work shift.

Even in full-swing production, variances existed from warplane to warplane on the same assembly line. Some parts, like wing-fuselage fairings, were shipped undrilled, to be hand-fitted on an airplane.

So the next time you see a pristine restored B-17, ponder the many-layered miracle of production that led to its completion in the war years. It was never a frozen design, and it participated in modifications before final delivery to make it the most current iteration of the basic airplane.