Soon numbers of the submarines made their way to the waters surrounding the British Isles, where they torpedoed merchant vessels taking food and supplies to Great Britain and France.  The vessels sunk were chiefly British, though some were neutral.

PROTECTION AGAINST SUBMARINES.—­Large war ships were protected from submarines by keeping them in a mine-protected area until there was need for them at sea.  At sea they were protected largely by the patrol and scouting operations carried on by lighter and faster vessels.  To reduce the danger to merchant vessels from submarines, harbors and sea lanes were protected by mines and by great nets made of heavy wire cables.  The seas in the immediate vicinity of Great Britain were patrolled by thousands of small, swift vessels constantly in search of U-boats.

ATTEMPTED BLOCKADE OF GREAT BRITAIN.—­In February, 1915, Germany declared a blockade of the British Isles.  Under an actual blockade she would have the right to prevent neutral vessels from trading with Great Britain.  But inasmuch as it was not possible to take seized neutral ships to German ports, the submarines would sink them, often without providing for the safety of the passengers and crews.  The ultimate object of this course of action was so to reduce the world’s shipping as to make it impossible for Great Britain to be supplied with the food or other materials that would enable her to carry on the war.  This method of warfare, however, was contrary to the well established rules of international law.  Against it the United States and other neutrals made vigorous protests.

THE LUSITANIA.—­The most notable loss by submarine attack was that of the “Lusitania,” sunk without warning off the coast of Ireland on May 7, 1915.  Nearly twelve hundred lives were lost, including many women and children.  One hundred and fourteen of those lost were Americans.  An advertisement had been inserted in the papers warning passengers not to travel on Allied ships, but no one believed that Germany would go so far in violation of international law as to torpedo, without warning, a passenger vessel carrying civilians of neutral as well as of warring nations.  The people of the whole civilized world were horrified by the deed.  Germany’s attitude is shown by the fact that medals were struck commemorating the act, and the commander of the submarine was rewarded.

President Wilson wrote a series of notes to the German government insisting that Germany conduct her warfare in accordance with international law.  This resulted in a promise by the German minister to the United States, that liners would not be sunk by German submarines without warning and without safety to the lives of noncombatants, provided that the liners did not try to escape or offer resistance.