Question...

As well she should for it or any other encyclopedia in any class at anything more than a primary school level - or informal chatting on a message board like this most of the time. In this case, it's good enough for our purposes rather than needing to look through primary diocume5tns or good secondary sources like Morison.

Well that last bit is very true. Now they could have also left them to wither away, due to the fact the japanese navy was by then all but sunk, but of course they wanted the island for an airbase, as this did save countless airmens lifes who before could not obviously land on there, so once they had captured it, they used it for there bombers, as it was so close to the home islands. So they had to move quite quickly to keep up there time table for the expected invasion of the home islands, but once they had seen just how desperate and brave just quite small numbers of japanese troops fought, it made them think what would some million men be able to do in there own back yard, and hence of course the need to find another method to bring the war to a close, so they tried to use massive air power to flatten there citys, and then the two nukes

But you are right that the defences above ground and near the beaches were for the most part wiped out due to the fierce naval bombardment (and the air attacks to), its just they had created a masterpiece of underground tunnels, chambers and defences, which no amount of naval bombings were going to destroy, as in most wars its down to the poor bloody infantry (and marines) to take.