[Graham Boak]

If it was still in good condition there'd be no reason to label it as "Weary". All aircraft have fixed structural lives, and the more they are used the nearer they approach failure. Nowadays this is closely monitored by the Fatigue Index, but before this came into use coarser methods of judgement were used. I don't know what methods were used by the USAAF or Luftwaffe, but some measure of total flying hours will have been involved. Even before reaching this limit, and accentuated by pulling high g, they can suffer structural warping. On a lower level, panels get bashed so that they don't fit as well as they used to. Gaps and steps appear. Skins get dented. This increases the drag. It becomes clear that this particular airframe is slower than its squadron mates. It doesn't accelerate as well, it doesn't climb as well, it doesn't turn as well, perhaps it's (comparatively) a bit of a pig to fly. OK for use in training, or for hack flying, but you don't want to take it into combat.