A major problem is that even a limited invasion would require massive forces, including two full South Korean corps. And there is reason to question whether South Korea could sustain the effort. "In our wargames, it was not unusual for the equivalent of a corps to be destroyed in one week's fighting to achieve a single penetration, translating to tens of thousands of casualties," RAND noted.
Reference: War Games Prove Why America Cannot Afford A Second Korean War
I'd like to know what "(in order) to achieve a single penetration" modifies.
The forms of "in order to do something" are used as adverbs, modifying a verb phrase. "(in order) to achieve a single penetration" is being used to modify the noun "fighting", and I think that it is not correct because it should be used to modify a verb phrase.
I'd like to know where I'm wrong.