Iwo Jima was the rare instance where everyone on the island was a combatant. No civilians at all.
The Japanese had abandoned the banzai charge of Guadalcanal and replaced that odd strategy with building an underground city of bombproof tunnels. So all of the pre-invasion bombardment by ships and aircraft accomplished nothing.
The bombardment rid the island of any remaining foliage, which meant clear shooting for the snipers.
An Iwo vet (I’d known him my whole life, I think I’d known he was in WWII, but didn’t know any specifics) was all fired up about the upcoming movie (this was back when the movie release was imminent) and showed me has various war-related memorabilia, including a vintage map of the island.
He nonchalantly pointed the curved route of the buried bunkers. He was a field medic, and the Japanese snipers made them a priority, so he lasted about three days. It took him more than a year to recuperate from his wound.
Of the USMC who served in all theaters of WWII, nearly a quarter died on Iwo or as a result of the wounds. Nearly a third of WWII Marines who earned the Medal of Honor earned it on Iwo.
It’s often said to be 8 sq miles, but it’s shaped kind of like a football and is, at best, 4 miles n-s and 2 miles e-w. The veteran interviews I’ve seen referred to the black volcanic sand/soil at the landing site as being like walking in wet coffee grounds.