During the greater part of the year 1917, however, it was only possible to supply destroyers with a small number of _depth charges_, which was their principal anti-submarine weapon; as it became feasible to increase largely the supply of these charges to destroyers, so the violence of the attack on the submarines increased, and their losses became heavier. The position then, as it existed in the early days of the year 1917, is described in the foregoing remarks. The _result_ measured in loss of shipping (British, Allied, and neutral) from submarine and mine attack in the first half of the year was as follows in gross tonnage: January - 324,016 February - 500,573 March - 555,991 April - 870,359 May - 589,754 June - 675,154 Because of the time required for production, it was a sheer impossibility to _put into effect_ any fresh devices that might be adopted for dealing with submarine warfare for many months, and all that could be done was to try new methods of approach to the coast and, as the number of small craft suitable for escort duty increased, to extend gradually the convoy system already in force to a certain extent for the French coal trade and the Scandinavian trade. In the chapters which follow the further steps which were taken to deal with the problem, and the degree of success which attended them, will be described. CHAPTER III ANTI-SUBMARINE OPERATIONS The previous chapters have dealt with the changes in organization carried out at the Admiralty during the year 1917 largely with the object of being able to deal more effectively with the submarine warfare against merchant ships. Mention has also been made of the submarine problem with which the Navy had to deal; particulars of the anti-submarine and other work carried out will now be examined.