.
Neither of these needs could have been supplied save by America's
throwing her utmost energies into active participation in the war.
This was precisely the result of the proclamation of Feb. 1, 1917.
The United States at once broke off diplomatic relations, armed
her merchant vessels in March, and on April 6 declared a state
of war.

Having traced the development of submarine warfare to this critical
period, we may now turn to the methods and weapons employed by
both sides at a time when victory or defeat hinged on the outcome
of the war at sea.

Germany's submarine construction and losses appear in the following
table from official German sources, the columns showing first the
total number built up to the date given, next the total losses to
date, and finally the remainder with which Germany started out
at the beginning of each year.

After 1916 Germany devoted the facilities of her shipyards entirely
to submarine construction, and demoralized the surface fleet to
secure personnel. Of the entire number built, not more than a score
were over 850 tons. The U C boats were small mine-layers about 160
feet in length, with not more than two weeks' cruising period.
The U B'g were of various sizes, mostly small, and some of them
were built in sections for transportation by rail. The U boats
proper, which constituted the largest and most important class,
had a speed of about 16 knots on the surface and 9 knots submerged,
and could remain at sea for a period of 5 or 6 weeks, the duration
of the cruise depending chiefly upon the supply of torpedoes. In
addition there were a half dozen large submarine merchantmen of
the type of the _Deutschland_, which made two voyages to America
in 1916; and a similar number of big cruisers of 2000 tons or more
were completed in 1918, mounting two 6-inch guns and capable of
remaining at sea for several months. The 372 boats built totaled
209,000 tons and had a personnel of over 11,000 officers and men.
There were seldom more than 20 or 30 submarines in active operation
at one time. One third of the total number were always in port,
and the remainder in training.

-----------------------------------------------------------
| Boats | | Remainder
| built | Losses |(On Jan. 1 of year following)
------------|-------|--------|-----------------------------
End of 1914 | 31 | 5 | 26
1915 | 93 | 25 | 68