Complex sentence: Rome plows were first used in III Corps (Military Region III), though major land clearing operations--to destroy trees and other jungle fauna that could be used by enemy forces--did not commence until May 1967 with the arrival of the 169th Engineer Battalion.
Split into simpler sentences: Rome plows were first used in III Corps (Military Region III) to destroy trees and other jungle fauna that could be used by enemy forces. Major land clearance operations did not commence, however, until May 1967 with the arrival of the 169th Engineer Battalion.