Throughout history, coastal fortifications have guarded strategic seaports. And until recently, forts easily outgunned ships. Hence legendary British admiral Horatio Nelson’s quip—“A ship’s a fool to fight a fort.”

But you don’t have to fight a fort when you can just cut it off.

Arguably the greatest coastal fort ever was America’s Fort Drum, which guarded Manila Bay in The Philippines until Japanese forces surrounded it in May 1942.

Fort Drum had its origins in an earlier war—the now-obscure conflict between America and Spain in 1898. The Philippines was a Spanish colony at the time. On May 1 of that year, a U.S. Navy squadron infiltrated Manila Bay, sank or crippled the Spanish fleet and captured the archipelago.

U.S. military engineers made note of of Manila Bay’s weak coastal defenses and drew up plans to fortify America’s new colonial outpost in Asia.

A decade after the war, Lt. John Kingman of the Army Corps of Engineers recommended building a new fort built midway between the islands of Corregidor and Carabao near the mouth of the bay.

In a report dated July 18, 1908, Kingman proposed constructing a stout concrete blockhouse and gun platform and equipping it with two giant battleship turrets.

Between 1909 and 1913, engineers encased the existing rocky nub of El Fraile Island in enough concrete to erect a large, vaguely ship-shaped bastion. Fort Drum’s barracks, ammunition magazines and utility spaces lay inside concrete walls up to 36 feet thick.