of these cargo steamers, all experienced seamen, gave it as their opinion that two or possibly three was the maximum number.  The opinions thus expressed were confirmed later by other masters of merchant ships who were consulted on the subject.  It is to the eternal credit of the British Merchant Marine, which rendered service of absolutely inestimable value to the Empire throughout the war, that when put to the test by the adoption of the convoy system, officers and men proved that they could achieve far more than they themselves had considered possible.  At the same time it should be recognized how severe a strain was imposed on officers, particularly the masters, of vessels sailing in convoy.

The matter was kept constantly under review.  In February, 1917, the Germans commenced unrestricted submarine warfare against merchant ships of all nationalities, and as a consequence our shipping losses, as well as those of Allied and neutral countries, began to mount steadily each succeeding month.  The effect of this new phase of submarine warfare is best illustrated by a few figures.

During the last four months of 1916 the gross tonnage lost by submarine attack alone gave the following monthly average:  British, 121,500; Allies, 59,500; neutrals, 87,500; total, 268,500.

In the first four months of 1917 the figures became, in round numbers: 

British.  Allies.  Neutrals.  Total.

January       104,000     62,000    116,000    282,000
February      256,000     77,000    131,000    464,000
March         283,000     74,000    149,000    506,000
April         513,000    133,000    185,000    831,000

(The United States entered the war on April 6, 1917.)

NOTE.—­In neither case is the loss of fishing craft included.

It will be realized that, since the losses towards the end of 1916 were such as to give just cause for considerable anxiety, the later figures made it clear that some method of counteracting the submarines must be found and found quickly if the Allied cause was to be saved from disaster.

None of the anti-submarine measures that had been under consideration or trial since the formation of the Anti-Submarine Division of the Naval Staff in December, 1916, could by any possibility mature for some months, since time was necessary for the production of vessels and more or less complicated materiel, and in these circumstances the only step that could be taken was that of giving a trial to the convoy system for the ocean trade, although the time was by no means yet ripe for effective use of the system, by reason of the shortage of destroyers, sloops and cruisers, which was still most acute, although the situation was improving slowly month by month as new vessels were completed.