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Most Soviet equipment, both civilian and military, had poor build quality.
The books I have read suggest the LaGG's were... not very fast
The later Lavochkin La-5 / 7 were from part of the same design team and were outstanding in most respects. They ere fast. maneuverable, well armed...
The prototype LaGG-1 and LaGG-3 models were hand finished and optimized for performance figures.
There was a large difference between those results and the subsequent production airframes' performance in the field.
May be nice initially but would fall apart after some weeks. Planes were not suited for hot/humid climates, airframes start to disintegrate. BTW in Vietnam almost every other assault gun would have been better than the M16 - the small caliber bullets were ill-suited for jungle warfare due to lack of penetrative power. Plus the reliability issues it suffered due to the conditions and lightweight built.I bet our Pacific P-40 and P-39 drivers would have accepted La-5s and La-7's any day of the week. I KNOW the Sherman guys would have traded for a T-34 at the drop of a hat.