I don't specifically want info about US forces but they're a good example of the supply problem you have, they're constantly fighting very far from home, and a lot of effort was put into designing a tank that could be easily repaired in the field; but they used this big single piece hull. So what happens when you take damage during a fight but you're not really knocked out? A panzerfaust or a Pak leaves some nasty scars that are definite weakpoints going forward but you can still drive home. I assume they don't just ship you a new cast hull to swap out and it's a single piece so you can't just unbolt the damaged bits and slap a new one in. For planes it's even worse since you can just weld some garbage plate to the side or dangle some sandbags and logs in front of the hole, you need to maintain low weight and an aerodynamic profile. So if you take some heavy MG fire into your wing and make it home how does the ground crew deal with that headache?
So if you take some heavy MG fire into your wing and make it home how does the ground crew deal with that headache?
Bullet holes could be plugged up, though if there was a risk to the structural integrity then a section of wing, or entire wing, could be replaced; aircraft were quite modular, maintenance units carried many spare parts.
In the USAAF maintenance and repair was divided into four echelons. The first covered the day-to-day servicing, inspections, and minor adjustments that kept squadrons flying, done by the squadrons that operated the aircraft. The second was more major servicing and repairs, such as replacement of engines, still carried out by the operational squadrons. The third and fourth echelons were specialist maintenance units responsible for more fundamental overhauls or repairs; with machinists, welders, metal workers, engine, hydraulic and electrical specialists they could perform extensive repairs.
If a bomber crashed away from its base mobile units could be despatched to either disassemble the aircraft and transport it to a repair depot, or even repair it in situ, including flattening out a temporary runway for it to take off again, a procedure documented in 'A Gal Named STELLA' from the USAAF Combat Film Unit. Pathé films also has a short film documenting mobile repair units, Keep 'em Flying. On the RAF side, the Imperial War Museum has footage of The Salvage and Repair of Avro Lancaster EE193, showing a Lancaster bomber that crashed on return to RAF Scampton being transported to No. 58 Maintenance Unit for repair.
Aircraft that were truly beyond repair (both allied and enemy) would have any usable parts removed, then taken to a Metal and Produce Recovery Depot for recycling, such as a facility at Cowley that inspired artist Paul Nash.
I can speak for tanks, at least in the Red Army. There was a standardized list of damage a tank could sustain that determined whether or not it was worth saving.
A tank that was burned out was destined for the scrap heap, as was a tank with major damage to any armour plate. What counted as major damage varies, but a crack that reached the edge or a crack that spanned 2/3rds of the plate was too much, as was a deep enough dent that it impeded the function of a tank. Holes were also a big deal: little ones were okay on their own, but a clustering of breaches within 450-500 mm of each other (depending on the size) or one breach that affected more than a third of the area of the plate were considered major. Tanks with damage greater than that but still salvageable were shipped to a factory, where it might be more economical to transplant the components into a new tank rather than try and repair the old hull.
The nature of the repair depended on the damage, a small enough crack could just be welded over, but a large crack or breach would have to be covered with a patch or a plug.
http://www.tankarchives.ca/2019/06/temporary-reinforcement.html