This proposal was approved by the Admiralty and was put into force as soon as the necessary organization had matured. Escorting vessels had with difficulty been provided, although in inadequate numbers. The first convoys sailed towards the end of April, 1917. The system may be described briefly as follows. The convoys all put into Lerwick, in the Shetland Islands, both on the eastward and westward passages, so that Lerwick acted as a junction for the whole system. From Lerwick, convoys to Scandinavia left in the afternoon under the protection of two or three destroyers, and, with some armed patrol vessels in company up to a certain stage, made the Norwegian coast at varying points, and there dispersed, and the destroyers then picked up the west-bound convoy at a rendezvous off the Norwegian coast shortly before dark, and steered for a rendezvous between Norway and the Shetland Islands, where an escort of armed patrol vessels joined the convoy at daylight to assist in its protection to Lerwick. From Lerwick convoys were dispatched to various points on the coast of the United Kingdom; those making for southern ports on the East Coast were escorted by a force composed of some of the old "River" class or of 30-knot class destroyers, and trawlers belonging to the East Coast Command based on the Humber, and those making for more northerly ports or ports on the West Coast were escorted merely by armed patrol vessels, as the danger of submarine attack to these convoys was not so great. The main difficulty was the provision of the destroyers required for the proper protection of the convoys, and to a lesser degree the provision of armed patrol vessels of the trawler, whaler, or drifter types.