Honouliuli National Historic Site preserves the site of Hawaiʻi’s largest and longest-operating Japanese internment camp during World War II, which later became the islands’ largest prisoner of war camp. Opened in 1943 in an isolated gulch near Ewa and Waipahu, it was the only Hawaiʻi internment site built specifically for prolonged detention. Run by the U.S. Army, the camp held civilian internees and, over the war years, more than 4,000 prisoners of war and detainees of several nationalities. After closing, it was largely forgotten until its rediscovery in 2002; its later federal designations recognize its central importance to understanding wartime internment in Hawaiʻi.