I'm one of the ones who had never heard of it.
Aided by the rugged terrain, their careful preparation, and new tactics, the Japanese would inflict more than twice as many casualties on the Marines on Peleliu as they had on Tarawa. Proportionally, Marine casualties on Peleliu equaled those suffered on Iwo Jima. Iwo is well known. Peleliu is all but unknown. The 1st Marine Regiment, commanded by Col. Lewis “Chesty” Puller, who was already a legend in the Corps, suffered the brunt of the casualties. The Regiment’s 1st Battalion had an astounding casualty rate of 71 percent, 2nd Battalion 56 percent, and 3rd Battalion 55 percent. Headquarters Company, usually well behind the front lines and presumably in a much safer environment, had a casualty rate of 32 percent. How the regiment remained operational is something to contemplate. . . .
Instead of the three or four days of fighting that had been anticipated, the Marines were fighting for more than a month. Ultimately, the three regiments of Marines — the 1st, the 5th, and the 7th — suffered 6,526 casualties on Peleliu.