m the horizontal and these two
instruments, lit up by electric lamps, showed it at once. There was a
big dial, with a long green hand, which also marked the depth of the
sub; but that was an insensitive and rather slow-acting gauge--all right
for the crew to look at from half the length of the sub, but not fine or
quick enough for the diving-rudder man.

He was the busy man while we were under water. The others could now and
again grab a moment of relaxation from their tenseness, but while the
sub was moving the diving-rudder man never took his eyes off the little
brass scale with the electric light playing on it. Stop and consider
that our sub had only to get a downward inclination of ever so little
while running hooked-up under water, and in no time she would be below
her lowest safety depth of 200 feet, where the pressure is 7 tons to
every square foot of her hull. And should she collapse there would be no
preliminary small leak by way of warning. She would go as an egg-shell
goes when you crush it in your palm. Plack!--like that--and it would be
all over. Above this same middle compartment, the smallest and most
crowded of all, up through the grilled spaces of a steel grating, we
could see the wide feet and boot-legs of the man who held the ship to
her compass course; and for a wheel, we knew, he was holding a little
metal lever about as long and thick as his middle finger, with a little
black ball about as big as the ball of his thumb on the end of it.

To the right of the foot of the conning-tower ladder stood the
ballast-tank man; and when the captain from the foot of his periscope
gave the word--after first looking forward, aft, and to each side of him
to see that all hands were at their proper stations--it was the
ballast-tank man who went violently at once into action. He grabbed a
big valve and gave it a twist; grabbed another and gave it a twist; and
another, and one more; and, standing near by, we could hear--or thought
we could--the in-rush of great waters.

[Illustration: In the engine-room of a submarine. The Diesel engines,
driven by crude petroleum, propel the ship on the surface. Electric
motors supply the power when running submerged.]

A man got to wondering then what would happen if this chap got his
valves mixed. But a look around showed every lever and every valve,
everything marked with its own name and number. Nothing was left
unmarked--in deep-cut black lettering on brass plates generally,