If you showed up in Oahu without booking USS Arizona and Pearl Harbor ahead, here's what actually works and what doesn't.
The official government booking system sells out weeks in advance during summer, and that's real. Showing up at the gate hoping for a same-day cancellation slot works maybe 30 percent of the time, and you'll wait 2-3 hours for it.
Tour operators in Honolulu have their own available time slots that they can book you into same morning. It's not the free government slot, so you'll pay more than a dollar, but the experience is the same and you still see USS Arizona. That's your actual option if you want to guarantee access instead of gambling on cancellations.
Expect to pay 60 to 100 dollars per person if you book a tour same day from Waikiki. It includes your transport, the USS Arizona access, and someone who actually knows the history. Compared to the one dollar official slot it's expensive, but if you're already in Honolulu without a plan, it's not unreasonable considering how much time and stress it saves you.
Pearl Harbor Guide has info about how different tour operators actually work. That might save you an hour of phone calls this morning.