Some lyric interpretation:
"Clothes of Brass" - reference to the exterior of Submarines, Brass fittings used for its resistance to corrosion.
"Hair of Brown" - the seaweed caught around the upper half of the submarine as it appears.
"Seldom need to breathe" - subs supply their own air and very infrequently need to resurface.
"Don't need no wings to fly" - wings not needed to fly through the ocean.
"and a heart of stone" - Uranium, the stone that powers the nuclear reactor which powers the vessel.
"and a fear of fire and water" - the 2 most deadliest things that can happen to a submarine, fire burns up the oxygen and everyone dies, water in reference to a hull breach, which leads to pressure loss, and everyone dies.
"Who am I?" - a Submarine.