Several ingenious inventions having sound as their basis were introduced. Of these the microphone, enabling the listener to detect the rhythm of submarine motors when submerged, is undoubtedly the most important. The télémétriste and the hydrophone, somewhat similar contrivances, were fitted on certain ships of the French Navy. The convoy system of gathering together a group of merchantmen and conducting them through the danger zone was merely the revival of a venerable institution. Its modern application met with considerably greater success than was often evident in the past. The First Dutch War of 1652–4, for instance, consisted very largely, so far as England was concerned, of attacks on convoys. The necessity for protecting them was responsible for four of the seven battles fought. Beginning in a comparatively small way, the idea of shepherding merchant shipping was gradually enlarged until few vessels sailed overseas unattended. The system was extraordinarily successful. Before it was introduced nearly 10 per cent. of Britain’s food ships were sent to the bottom by an enemy bent on starving England into submission. When the vessels were assembled and protected only 1 per cent. was lost, and 26,000,000 tons of foodstuffs were brought over from different parts of the world, in addition to 35,000,000 tons of munitions of various kinds. The whole of the Argentine wheat crop was transported to Great Britain, France, and Italy in 307 ships, of which only one was lost through enemy action. The celebrated ‘Q’ ships are mystery ships no longer. The idea of these decoy vessels was obviously suggested by the raider _Möwe_, which resembled a tramp and was really a powerfully armed fighting unit of the German Navy, as many a captain of the Mercantile Marine found to his cost. Officered and manned by volunteers, the avowal of Sir Eric Geddes that the crews were made up of “the very bravest that our sea service can produce” was more than a mere figure of speech. No fewer than eight of their commanders won the V.C.