 Naval bombardment prior to amphibious assault at Iwo Jima was only slightly more effective than at Peleliu, but at Okinawa the preliminary shelling was much improved.Frogmen performing underwater demolition at Iwo Jima confused the enemy by sweeping both coasts, but later alerted Japanese defenders to the exact assault beaches at Okinawa.American ground forces at Peleliu gained experience in assaulting heavily fortified positions such as they would find again at Okinawa.