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.