Here are two books that shed some light on the utter shambles that was a major feature of the WW2 production of war materiel and spares - and the logistics of getting that materiel and those spares to the front line, during the War.
The history of the AAF during WW2 (Chapter 10 - The Production Record is the most pertinent chapter here)
The Logistics of War - 1941-1955
WW2 was a constant sharp learning curve for all involved, and the Americans ability to manage industrial production for war equipment was sorely tested many times during the War.
Time after time, orders were placed for equipment by military divisions, only for those orders to be doubled or quadrupled a month later - or cancelled completely as new designs took precedence.
It was a constant struggle to try and balance the raw material production and the factory production to meet the expected demand - and a struggle to try and get a handle on the amount and type of spares needed - and to then get them to the front lines.
In vast numbers of cases, early on in the War, equipment was cannibalised to keep other items of equipment operating. It was the easiest and quickest way of keeping aircraft going.
In the early part of WW2, this cannibalisation was a major problem, resulting in huge numbers of aircraft becoming unserviceable due to them being stripped to keep other aircraft in the air.
It was not until serious changes were made to the level of spares production (around late 1942), that the spares shortages started to become alleviated.
In many cases, sea shipping was the primary delivery method for all spares. Huge storage depots were established near ports and in secure close inland areas, as beachheads progressed further into enemy territories.
Trucks and rail were the secondary delivery methods, moving spares and materiel from the base storage depots.
Spares were only delivered by air as a last resort, if excessive numbers of vital aircraft and equipment were being stood down, due to a critical spares shortage.
In the SW Pacific, the U.S. had major problems with supply bases not being able to keep up, with the fast island-hopping progress of the frontline troops.
As a result, much war materiel and spares were rendered useless due to supplies arriving before warehouses could be built - so the materiel and spares were stored in the open and suffered badly from exposure to the weather - which was usually wet, salty, and humid throughout much of the Pacific region.
On one Pacific island near Vanuatu, a U.S. storage facility for war materiel in 1943, contained the mind-boggling value (in 1943 dollar terms) of US$9M worth of new stores and spares.
However, a very large part of this huge stores and spares stockpile was reduced to worthlessness - firstly, by poor storage in the open - and secondly by the fact that the U.S. troops had leap-frogged so far ahead of the island, it became nearly useless as a supply base - and it was more efficient for shipping to bypass the island, and deliver new supplies and spares to up near the front lines, that were by now, a long way away.
In Europe, supply problems were compounded by inadequate records showing what materiel and spares was located on each ship that arrived - resulting in a mad scramble to try and find the location of vital spares, ammunition and equipment, that was crucial to the military advance.
All in all, the entire Second World War constituted major lessons in equipment production, management, delivery, and logistics for the Allies.
One of the most interesting statistics of WW2 aircraft production was the fact that as the War progressed, the average size of Allied aircraft being produced, increased substantially - while the average size of the Axis aircraft produced, reduced in size.
This was due to an emphasis on production of 4-engined aircraft such as bombers and heavy transports amongst the Allies, while the Axis production retreated to defensive aircraft such as single-seat fighters and smaller attack aircraft, as the War started to go badly for them.