Complex sentence: Iranian helicopters (AH-1 Cobras) also joined the battle, destroyed several dug-in Iraqi tanks, but they were outnumbered by Iraqi helicopters which inflicted heavy losses on the Iranian tanks.
Split into simpler sentences: Iranian helicopters (AH-1 Cobras) also joined the battle, destroyed several dug in Iraqi tanks. But they were outnumbered by Iraqi helicopters which inflicted heavy losses on the Iranian tanks.