phut-phut, and the submarine boat began its long journey down Long
Island Sound. The boat started in with her deck awash--that is, with two
or three feet freeboard or of deck above the water-line. In this
condition she could travel as long as her supply of gasoline held
out--her tanks holding enough to drive her 560 knots at the speed of six
knots an hour, when in the semi-awash condition; the lower she sank the
greater the surface exposed to the friction of the water and the greater
power expended to attain a given speed.

As the vessel jogged along, with a good part of her deck showing above
the waves, her air ventilators were open and the burnt gas of the engine
was exhausted right out into the open; the air was as pure as in the
cabin of an ordinary ship. Besides the work of propelling the boat,
the engine being geared to the electric motor made it revolve, so
turning it into a dynamo that created electricity and filled up the
storage batteries.

[Illustration: LAKE'S SUBMARINE TORPEDO-BOAT _PROTECTOR_
This boat is designed to travel on the surface, or fully submerged, or
on the ocean's bottom. She is provided with wheels that support her when
on the bottom, and with a divers' compartment from which divers can work
on submarine cables or the enemies' explosive mines.]

From time to time, as this whale-like ship plowed the waters of the
Sound, a big wave would flow entirely over her, and the captain would be
looking right into the foaming crest. The boat was built for under-water
going, so little daylight penetrated the interior through the few small
deadlights, or round, heavy glass windows, but electric incandescent
bulbs fed by current from the storage batteries lit the interior
brilliantly.