[ACE-OF-ACES]

Some of the field kits were performance enhancing and others added weight for the sort of hybrid roles that frontline fighters often flew.

Added to this are the unauthorized modifications.

On that note

The authorized mods sent to field units typically were tested in the rear before being sent to the field units

A good example is the Allied 150 octane engine modification (kits) were tested in the rear before being used in the field

And instrumented performance tests were preformed and the data collected for us to use in a comparison

Now I think we have all heard some of the stories about the un-authorized mods done in the field

I know I have heard some stories about the P-47 mechanics making un-authorized changes

But can anyone point to a real book reference that goes into more detail than what the mechanic said he did in the movie Kelly's Heroes with regards to making his Sherman tank faster?