How do submarines rise and dive? Do they require outside energy (as in
the electricity needed to run an aircompresser to pressurize an air
compartment used to later blast out the water from the ballast tank) or
can they function without added energy?
Here's the challenge...will it work?

Is it possible to get a barrel filled with air ( barrel A) to
sink using another barrel( barrel B) that fills with water and Once
the contraption is at the bottom flood the air filled (barrelA) with
water and somehow raise the contraption to surface to do another sink
rise cycle. My thoughts were that you could collect all the air that
is forced out of both barrels during their taking on water phase and
direct it into a smaller high pressure container to be used to later
blast out water for the rise to surface.

What if you started with all three containers at high pressure? Are
you losing energy during each cycle? Is this a perpetual motion
machine?......(Which I understand and believe are not possible) OR does
it simply not work indefinatly?