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The F4U and P-47 were extremely rugged aircraft. From toughest to weakest, I would order them like this.
P-47
F4U
F6F
Fw-190
P-38
P-51
The only reason I put the P-38 above the P-51 is it has two engines.
Thanks for the quick response guys. By toughness, I mean being able to take damage from enemy fire. I'm afraid the game does use a very generalized assumption for damage values. While things like self sealing tanks are specifically added to the toughness value, they are incorporated in to the overall value.