The "Arsenal of Democracy" truly was that.
Images of the Boeing Seattle Factory in World War II
Boeing B-17F Flying Fortresses on the Seattle production line.
Boeing B-29 Superfortresses on the Everett production line.
To understand how important it was, over 1/2 of all Boeing B-17s produced were lost in combat - then add in another 1000 or so destroyed as a result of training accidents - and you can understand how important making MORE than what you need helped win the war against the Axis powers - they only produced just enough to what they thought they needed - and it was never enough.
The United States Army Air Forces - USAAF - was part of the ground forces. All regular officers, with their specialty being flying. The Concept of precision daylight bombing to destroy key war industries, thus cripple the enemy by destroying the items of war, was a big concept in the 1920s and 1930s.
The Boeing B-17 - a private venture based on this assumption of a strategic bomber - was the results of the early war thinking of the "bomber will always get through" mentality. And this was fact - since every bomber built in the early 30s was 25 to 50 mph faster than the fighters!
The fighter plane was there to destroy the enemy aircraft - not designed or thought as even necessary to escort the bombers.
A PDF of all air transport aircraft lost during World War II by type of aircraft and by year. Table 204 from Air Transport Command Office of Statistical Control.
In the early part of the war the USAAF flew missions into France and along the edges of Germany. Only 25 missions were needed to go home.
| # | Mission Date | City | Mission Target |
| 1 | 7-Nov-42 | Brest, France | U-boat pens |
| 2 | 9-Nov-42 | St. Nazaire, France | U-boat pens |
| 3 | 17-Nov-42 | St. Nazaire, France | U-boat pens |
| 4 | 6-Dec-42 | Lille, France | Locomotive works |
| 5 | 20-Dec-42 | Romilly-sur-Seine, France | German airfield |
| 6 | 3-Jan-43 | St. Nazaire, France | U-boat pens |
| 7 | 13-Jan-43 | Lille, France | Locomotive works |
| 8 | 23-Jan-43 | Lorient, France | U-boat pens |
| 9 | 4-Feb-43 | Emden, Germany | War Plant |
| 10 | 14-Feb-43 | Hamm, Germany | Rail yard |
| 11 | 16-Feb-43 | St. Nazaire, France | U-boat pens |
| 12 | 26-Feb-43 | Wilhelmshaven, Germany | Naval base |
| 13 | 27-Feb-43 | Brest, France | U-boat pens |
| 14 | 6-Mar-43 | Lorient, France | U-boat pens |
| 15 | 12-Mar-43 | Rouen, France | Rail yard |
| 16 | 13-Mar-43 | Abbeville, France | Airfield |
| 17 | 22-Mar-43 | Wilhelmshaven, Germany | Naval base |
| 18 | 28-Mar-43 | Rouen, France | Rail yard |
| 19 | 5-Apr-43 | Antwerp, Belgium | Aircraft factory |
| 20 | 16-Apr-43 | Lorient, France | U-boat pens |
| 21 | 17-Apr-43 | Bremen, Germany | Focke-Wulf Factory |
| 22 | 1-May-43 | St. Nazaire, France | U-boat pens |
| 23 | 4-May-43 | Antwerp, Belgium | Ford Truck factory |
| 24 | 15-May-43 | Wilhelmshaven, Germany | Naval base |
| 25 | 17-May-43 | Lorient, France | U-boat pens |
"Twenty-five doesn't sound like much until you start
flying them."
— Capt Robert Morgan of the Memphis Belle
Later, as the Luftwaffe became less of a threat, plus personnel shortages, the mission count was upped to 30 then to 35. This was only for the 8th AF. Different air forces has different mission limits (fighter pilots flying out of England had 50 missions). The 15th AF flying out of Italy had 50 missions as a default minimum number to fly before a bomber crew member could be sent home.
In the early part of the war the average loss rate was 7% for B-17s and B-24s. Considering that 25 missions * 7 percent chance of being shot down equals 175% - (bad math but it makes the point) that the chances of finishing a tour was remote early on.