The OR&L converted many of its coaches to "can car" service in the 30s, hauling pineapple cans from the manufacturing plant to the canneries. When WW2 came along, many, if not all, were converted back to passenger service with the sliding side doors intact. Some of the cars, at least, had benches running length-wise rather than the usual coach style of seating.
The US Military had an extensive three-foot gauge rail network of its own at various installations on O'ahu and interchanged with the OR&L.
Ed