"You want to get a sub right. A sub is a ship modelled different from
most ships, of course, and built stronger to stand pressure, but only a
ship, after all, with special tanks in her. She's on top of the water
and wants to go down. Good. She fills her tanks and down she goes. She's
down and wants to come up. All right. She empties her tanks and up she
comes. She's got to. She couldn't stay down with her tanks empty if she
wanted to--not unless she blew a hole in her side, or left her hatches
open.

"Of course if her tanks don't work right! But we showed you three
different ways to-day how she can beat that game. And anyway, no matter
what happens, unless you're cruising deep, it's only a few feet to the
top. Not like a crazy aeroplane a thousand feet up in the air! Something
happens in an aeroplane, and where are you? With a busted stay or bamboo
strut and you a mile in the air, where are you? Volplane? Maybe. But if
you didn't--down you'd come atumbling like a hoop out of the clouds.
That's 90 per cent--yes, maybe 99 per cent--of the submarine game: See
that everything is right mechanically with your sub, then get a competent
crew and--well, you're ready."

That is for the submariner's point of view. As for the danger from a
shore-goer's point of view: Ashore we make the mistake, perhaps, of
thinking of a submarine as a heavy, logy body fighting always for her
life beneath an unfriendly ocean; whereas she is a light-moving easily
controlled creature cruising in a rather friendly element.

The ocean is always trying to lift her atop and not hold her under
water. A submarine could be sent under with a positive buoyancy so
small--that is, with so little more than enough in her tanks to sink
her--that an ordinary man standing on the sea bottom could catch her as
she came floating down and bounce her up and off merely by the strength
of his arms. Consider a submarine under water as we would a toy balloon
in the air, say. Weight that toy balloon so that it just falls to earth.
Kick that toy balloon and what does it do? Doesn't it bounce along, and
after a few feet fall easily down again, and up and on and down again?

Picture a strong wind driving that toy balloon along the street, and the
balloon, as it bumps along, meeting an obstacle: Will the balloon smash
itself against the obstacle, or what will it do? What that balloon does
is pretty much what a submarine would do if, while running along full
speed under water,