This museum on Schofield Barracks remembers the proud achievements of the US Army’s 25th Infantry Division, nicknamed 'Tropic Lightning.' The division was activated in 1941 in Hawaii. The museum has displays from the various campaigns that the 25th served in, including WWII, and the occupation of Japan, Korea, Vietnam, Afghanistan and Iraq. Admission is free and the general public is welcome, but if you don't have a military ID there's a bit of rigmarole to get in.
You'll need to enter Schofield Barracks' Lyman Gate on Kunia Rd with ID for everyone in the car, car registration and insurance (rental-car agreement) to obtain a visitor pass.