questionable that improvements in or alternatives to internal combustion engines will favor the increase of power in relation to weight, and so will tend to the production of vessels of higher speed. The comparatively slow speed of existing submarines as compared with destroyers and torpedo-boats of ordinary types admittedly involves serious limitations in their chances of successful attack on vessels under way, and higher surface speeds are desirable.
Concurrently with the construction of submarines, experiments have been made in this country and abroad to discover the best means of defence against this method of attack. Here again authentic details are necessarily wanting, since the various naval authorities naturally wish to keep discoveries to themselves. It is very probable, however, that published accounts of tests between swift destroyers, vedette boats and submarines are not altogether inaccurate, and according to these accounts the periscopes of submarines have been found useful by assailants as the means of determining the position of the submarines, and aiding their entanglement. Comparatively limited structural damage to a submarine in the diving condition may be accompanied by an inflow of water in a short period, which will result in the loss of the vessel. The accident to Submarine A 1, which was struck by a passing mail steamer, illustrates this danger. It is reasonable to accept the published reports that large charges of high explosives exploded at a moderate distance may have a serious effect against submarines, and cause them to founder. Their small reserve of buoyancy in the diving condition makes them specially liable to risks of foundering rapidly, and little more than a crevice may practically fill the interior with water in a very short time when the vessel is submerged even to a moderate depth. On the other hand, reports which have appeared of the manœuvres in France and elsewhere, when attacks have been made by submarines on vessels at anchor or under way, show a considerable percentage of successes. Such exercises are valuable no doubt for purposes of training, but under peace conditions it is necessary to avoid the risks of damage to submarines, which might easily become serious if the defence were pressed home as it would be in war. When the officers and crews of submarines know that they will be treated more considerately than in real warfare, they will naturally take chances, and make attacks involving possible destruction under the conditions of a real action. In short, naval manœuvres in this department, while they may be useful in increasing the skill and confidence of officers and men in the management of submarines, can be no real test of fighting efficiency.
Submarines and airships have certain points of resemblance, and proposals have been made repeatedly to associate the two types, or to use airships as a means of protection from submarine attacks. One French inventor seriously suggested that a captive balloon attached to
