apportioned to each man according to
his activities and according to the size of the boat.

It is unnecessary to clear the air artificially during a short
submersion, but during prolonged ones it is advisable to begin doing
so at an early hour to prevent the carbonic acid gas from gaining a
disproportionate percentage, as it becomes then more difficult to
control, and it is obvious that it is impossible to dissipate the
fumes of cooking, the odors of the machine oil, and the breath of the
crew.

Taken altogether one can live comfortably underseas, although there is
a certain discomfort from the ever-increasing warmth produced by the
working of the electrical machinery, and from the condensation created
by the high temperature on the surface of the boat plunged in cold
water, which is more noticeable in winter and in colder regions.

It is interesting to observe that the occupations of the crew
determine the atmospheric conditions: the quantity of air required by
a human body depends entirely on its activity. A man working hard
absorbs in an hour eighty-five liters of air. Besides the commander,
who is vigorously engaged in the turret,--as will be hereafter
described,--the men, employed on the lateral and depth steering, and
those handling the torpedo tubes, are doing hard physical work. The
inactive men use up a far smaller quantity of air, and it is
ascertained that a man asleep requires hourly only fifteen liters of
air. A well-drilled crew, off duty, is therefore expected to sleep at
once, undisturbed by the noise around them, and their efficiency is
all the greater when the time comes to relieve their weary comrades.
We had a wireless operator on board whose duties ceased after
submersion, and he had so well perfected the art of sleeping that he
never cost us more than fifteen liters of air, hourly, underseas.

The length of time that a U-boat can remain under water depends, as we
stated above, on the atmospheric conditions at the moment of
plunging, and on the amount of oxygen and chemicals taken on board. We
can stay submerged for several days, and a longer period will probably
never be necessary.

The distance of vision varies somewhat under water, as we look out
from the side windows cut into the steel armor of the commander's
conning tower. We can naturally see farther in the clear water of the
deep ocean than in the turbid, dirty water at the mouth of a river,
and the surface of the water-bottom has a d