I remember reading in "Strong men Armed" during the Peleliu landing, the U.S.S. Portland fire control director visually spotted
a Japanese gun crew with field artillery piece emerge from a cave mouth to fire on the landing 1st Division marines.
Three or four times, the Portland fired into the hillside where the cave was located and each time the gun crew w/artillery came
back out and fired. Frustrated, the Portland's gunnery officer was heard to exclaim "You can put all the steel in Pittsburgh on it
and still not get it."