The assistance from the United States that it was hoped was now in sight made the prospect of success following on the adoption of the convoy system far more favourable, and preparations were put in hand for the institution of an ocean convoy system on a large scale. In order to gain some experience of the difficulties attending the working of cargo ships, directions were given for an experimental convoy to be collected at Gibraltar. The necessary officers were sent out to Gibraltar with orders to assemble the convoy, to instruct the masters in the work that lay before them, and to explain to them the system of sailing, the manner in which the convoy would be handled, and the protection that would be afforded. This naturally took time, and the convoy did not arrive in England until after the middle of May. The experience gained showed, however, that the difficulties apprehended by the officers of the Mercantile Marine were not insuperable, and that, given adequate protection by cruisers and small fast craft, the system was at least practicable. It was accordingly decided to put it into operation at once, and to extend it as rapidly as the increase in the numbers of our destroyers and sloops permitted. The North Atlantic homeward-bound trade was brought under convoy in May, 1917, and the Gibraltar homeward-bound trade in July, but for some months it was impossible to provide for the institution of a complete convoy system. At first some 40 per cent, of the homeward-bound trade was convoyed. Then the system was gradually extended to include first 60 per cent., then 80 per cent., and finally 100 per cent, of the homeward Atlantic trade and the trade from Gibraltar, trawlers being used as escorts for the Gibraltar trade, as the majority of the ships therein engaged were slow. But trawlers are unsatisfactory escort vessels. In the early stages of the convoy system difficulties were experienced from the fact that all the available destroyers and most of the sloops were used as escorts, with the result that the ships not under convoy were left with but little protection. CHAPTER V THE CONVOY SYSTEM AT WORK As has been mentioned in Chapter II., the first ships to be brought under a system of convoy were those engaged in the French coal trade and in the trade between Scandinavia and the United Kingdom. In the case of the _French coal trade_, commencing in March, 1917, the steamships engaged in the trade were sailed in groups from four different assembly ports, viz.: Southend to Boulogne and Calais. St. Helens to Havre. Portland to Cherbourg. Penzance to Brest. Between Southend and Boulogne and Calais the protection was given by the vessels of the Dover Patrol in the course of their ordinary duties, but for the other three routes special escort forces were utilized, and daily convoys were the rule. Owing to the great demand for coal in France, sailing vessels were also used, and sailed under convoy from several of the south-west ports.