[Tom Houlihan]

In reality, I think that even with a full 30 day's bombardment, the effect would have been minimal.

As you pointed out, the defenders were in, as opposed to on, the island. I have walked through some of the tunnels there. Unless you had multiple shells landing in the same spot consecutively, excavating the terrain, nothing was going to happen. They were too deep.

The only real effect I can think of would have been psychological. That long a bombardment might have effected the minds of some of the defenders, but that's about it. I can't say whether that would be a good thing or not.