WITH ALL DUE RESPECT, It was the japs proving their fanaticism there that convinced us to use nukes, NOT their tunnels. I don't think Iwo Jima's caves held a candle to the tunnel complexes in Viet Nam. Cu Chi alone had 250 Kilometers of interconnected tunnels!
If Iwo Jima's complexes did compare, we didn't learn too much about tunnel warfare, considering all the expensive stuff that didn't work in Viet Nam. We tried blowing or plugging them up, pumping in gases and chemicals, sprinkling the entrances with stuff that killed them or helped us track them, we tried devices that sniffed out urine. We even tried using bedbugs that were supposed to get excited when they smelled sweat. (They couldn't tell WHOSE sweat they smelled!)
That book I keep harping about was an excellent read about all the "high tech" things the Army Warfare College (or some such name) developed and experimented with.
But it all came down this - the only thing that REALLY worked was a guy armed with a knife, small revolver, flashlight, and a rope tied to his leg, so they could drag him back out if something happened. These guys has a SET!
Most of those tunnels in Cu Chi are still there, except for the ones that were exposed by the arc light missions towards the end of our involvement. By that time, we had already been defeated by the pinkos at home.
BTW-My link doesn't go to the book, it goes to material from it with pictures that made it appear to BE the book.