They say that breaking up is hard to do!

Probably more of a topic for the eco-warriors in the group but of some interest to this old salt.
A lot of USN steel is stripped of most of the bad stuff and sunk in target practice or....transmogrified into museums.
Occasionally they are turned into reefs.

Subs are painstakingly recycled at a breathtakingly yuge cost.
Their reactor compartments are removed in one big piece, placed into an adult-proof container, and stored underground.

Brown wrapper Marus on the other hand are usually not very technologically interesting, and they do not glow in the dark.
Once they reach the end of their economic lifespan they become something of a liability.

Enter:
The world's most populous nation.....and submitted for your approval.....