e of
depth-bomb was developed and applied. This is one of the most efficient
methods of beating the submarine that has yet been found. Explosive
charges are fitted with a mechanism designed to explode the charge at a
predetermined depth below the surface of the sea. The force of the
explosion of a depth charge dropped close to a submarine is sufficient
to disable if not sink it, and American boats have been fitted with
various interesting means of getting these bombs into the water.

Smoke-producing apparatus was developed to enable a vessel to conceal
herself behind a smoke-screen when attacked by submarines and thus
escape. Several types of screen have been invented and applied in
accordance with the character of the vessel. After a study of the
various types of mines in existence, there was produced an American mine
believed to involve all the excellent points of mines of whatever
nationality, while another extraordinary invention was the non-ricochet
projectile. The ordinary pointed projectile striking the water almost
horizontally is deflected and ricochets. A special type of shell which
did not glance off the surface of the ocean was developed early in 1917
and supplied to all vessels sailing in the war zone.

The first year of the war saw also the development of the seaplane, with
the adaption to this vehicle of the air a nonrecoil gun, which permits
the use of comparatively large calibers, and of the Lewis gun. This year
saw also the completion of the latest type of naval 16-inch gun,
throwing a projectile weighing 2,100 pounds. Our newest battleships will
mount them. In this connection it is interesting to note that broadside
weights have tripled in the short space of twenty years; that the total
weight of steel thrown by a single broadside of the _Pennsylvania_
to-day is 17,508 pounds, while the total weight thrown from the
broadside of the _Oregon_ of Spanish-American War fame was 5,600 pounds.

The navy also went in vigorously for aviation and has done exceedingly
well. After the expansion of private plants had been provided for, the
navy decided to operate a factory of its own, and a great building 400
by 400 feet was erected in Philadelphia in 110 days at a cost of
$700,000. Contracts involving approximately $1,600,000 have been made
which will more than treble the capacity of this plant.

In addition to work of this sort and services including scores of
specialized activities, such as medical developme