Artificial reef is a real and useful purpose - can make a big difference
in fish populations, which are not doing well due to excess harvesting
in many locations.

With the military ships in particular, there are a lot of old sailors
who are happier to have the "old girl" buried at sea than cut up for
scrap. Much of the high-value scrap is removed in the preparation and
cleaning process.

It also generates income from divers who go out to dive on the ship,
either to see the ship, or for the fish and other life that soon grows
on it. In most cases groups of divers raise the money for getting the
things in place, though the Navy does cover some or all of the cleanup
cost - cleaning up their own mess.

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