Convoys worked for a number of reasons. Concentrating vessels in
convoys made them less visible to a submarine than they would have been
as individual travelers, and submarine commanders complained that the
ocean now seemed empty. There was little visibility from a submarine's
periscope, and, instead of an endless stream of individual ships to watch for,
the captain of the submarine now had the far less frequent opportunity of
spotting a convoy. When German attackers encountered convoys and their
armed escorts, only a brief assault was possible before the submarine itself
was placed in deadly peril as several enemy destroyers pummeled it with
depth charges. Contrary to the view of conservative British admirals, the
convoy forced the submarines to fight the British navy—and on highly
unfavorable terms. The best German commanders, or at least the most
aggressive, suffered the highest losses.
The Germans discovered that the entry of the United States into the
war—a certainty once Berlin ordered unrestricted submarine warfare—injured
their efforts quickly and painfully. The rapid arrival of more than thirty
American destroyers in Europe was a key factor in supplying an adequate
number of escorts. The United States seized interned German cargo vessels
when war was declared: thus, half a million tons of shipping from the
merchant German fleet shored up the beleaguered Allied forces.
By September 1917 the tide had turned. Most shipping in the busy North
Atlantic corridor went by regular convoy. Each month, more of the Allied
sea traffic came under the convoy system. Losses to the submarine continued,
but at a sharply reduced rate. By the war's last months, German
submarines were sinking only one merchant vessel for every four they had
destroyed in spring 1917. Frustrated commanders returned to port with most
of their torpedoes still on board.
World History
