On the outbreak of war, the Submarine Service, as did the surface fleet, added to its personnel by the use of Royal Naval Reserve officers, and "hostilities only" ratings, the latter being usually men with experience as motor mechanics or workshop engineers. These ratings were employed either in the depot ship workshops or in the engine-rooms of sea-going submarines, and they there justified their presence by the sound and keen work they performed under strange and often dangerous circumstances. The R.N.R. officers were used as watch-keepers and navigators in the boats, and their history in the war is shown in their long list of decorations and casualties. They were not expected to learn much of the technicalities of submarines--there were other officers aboard who could look after that side of the business--but in many cases they taught themselves far more than had been expected, with the result that they were able to substitute on occasions the regularly trained officers. Their chief duty, however, lay in watch-keeping and navigating: nothing could approach the air of calm detachment with which an R.N.R. would go forward to his bunk to turn in, after he had--half-way through his night-watch on deck--pressed the button of the diving alarm at sight of an enemy patrol boat close aboard, closed the lid, descended with a rush, and reported the cause of the alarm to the captain. By the time the captain had checked the descent and levelled the boat at sixty feet, the R.N.R. lieutenant would be snoring peacefully, the matter being out of his head once he had taken his decision to give the "crash-dive" order. All through the war we carried an R.N.R. officer aboard every sea-going submarine as a "third-hand," and the Service owes a very great deal to the help of these competent and loyal auxiliaries. The following is written of a combination of two or more true war incidents. It is intended to illustrate what the writer considers to be the true strategic use of patrol submarines. After 1916 the Submarine Patrol flotillas that watched the exit of the Heligoland Bight were given certain orders, which altered altogether their duties and their _raison d'être_. These were to the effect that no outward-bound ship of the enemy was to be attacked or fired at until a signal had first been made by the sighting submarine, to report such enemy's presence and movement; only homeward-bound ships could be fired at, and if outward-bound ships were seen, the reporting signal was to be made at all costs. This alteration detracted somewhat from the interest of submarine war, but it added largely to the strategic usefulness of our patrol boats. It is of no use to torpedo an enemy ship and thereby lose a chance for the Grand Fleet of cutting off the whole enemy force, and a torpedo fired meant that an hour or more of depth-charging would follow the shot, and prevent the signal being made before the news of the enemy's position had grown cold.