obsolete the huge costly leviathans that even the richest nations could ill-afford to maintain in the race for naval supremacy.

In Great Britain the opinion of those qualified to judge was nearly equally divided. The Blue Water School maintained that a numerically superior fleet of ships, capable of defence against aircraft, would meet the case, provided a supplementary division of airships and aeroplanes was ready to act in conjunction with the squadron. Battleships could keep the sea in all weathers, while aircraft were at the mercy of every hurricane.

On the other hand the supporters of the air fleet deprecated the need of a huge navy--using the word navy in the strict sense of the term. All the warships that Great Britain had at her command could not prevent the passage by night of airships and aeroplanes--either singly or collectively--across the comparatively short distance between the Continent and the East Coast of England, while by a judicious study of the barometer and climatic conditions generally the dangers of being overtaken by a heavy gale could be reduced to a minimum. Besides, had there not been instances of foreign aircraft manoeuvring over the East Coast naval ports at night during the progress of a terrible equinoctial gale that had caused, amongst other disasters at sea, the loss of several destroyers taking a doubtful shelter in the badly-protected Admiralty Harbour at Dover?

Up to the present time the result of the controversy in Great Britain was a compromise. Instead of spending a couple of million pounds upon a single battleship of between forty or fifty thousand tons, smaller ships were laid down and completed within eleven months. They were not pleasing to the eye. Even the "ironclads," ugly in comparison with the stately "wooden walls" of the early nineteenth century, were models of symmetry and grace beside the latest creations from the brain of the Chief Constructor of the Navy.

The modern battleships were vessels of but ten thousand tons displacement, or about the same as the "Anson" class of 1886. Their draught was, however, considerably less, being but twenty-two feet when fully manned and ready for sea. They were propelled by internal combustion heavy oil engines capable of developing 22,000 horse-power, the maximum speed being forty-two knots. The principal armament consisted of twenty-four six-inch guns, that for muzzle velocity, range, penetration, and bursting power of the projectile were more than equal to the fifteen-inch gun mounted on the later Super-Dreadnoughts of the United States Navy. The weight saved in engines, armament, and especially by the absence of coal, was devoted to additional armour. The battleships were veritable steel-clad vessels, for not only were the sides completely encased in Harveyized steel, but the upper decks were surmounted by a V-shaped roof capable of resisting the most powerfully-charged shell that airships could possibly carry.

Nor was the protection for submarine attack left unprovided for. The whole of the under-water surface was armour-plated, not merely by one skin but by two complete layers of steel, the thickest being on the inside. In the double bottoms thus formed, oil, the food for the motors, was stored. A powerful torpedo might fracture the outer armoured skin and release the oil in that particular section, but having the thickest plating inside it was considered almost a matter of impossibility for the latter to be holed and thus admit the burning oil--a source of danger that had long been recognized--into the vitals of the ship.

Submarine warfare, in the opinion of many naval experts, had had its day. At the height of five hundred feet a scouting aeroplane could easily detect the presence of a submarine so long as it was daylight. By night a submarine would be fairly safe from observation, but conversely her commander could not with certainty attack a hostile ship that had taken the precaution of manoeuvring with screened lights. In addition to the danger of mistaking friend for foe there was also the possibility, nay probability, of being unable to see the enemy's ship. It was, however, admitted that the submarine's chance was to attack either at dawn or sunset, with a fairly choppy sea running, and no aircraft to upset the calculations of the officer at the periscope.

Nor had the vast changes occasioned by the development of aircraft been confined to naval affairs. Fortifications, hitherto considered impregnable, were rendered untenable by reason of the danger from attack from above; and in this respect the reorganization of the Portsmouth defences might be taken as an example of what had to be done in other naval and military towns of the British Isles.

As is well known Portsmouth, the principal naval arsenal of the British Empire, is defended by a triple line of fortifications; while to prevent subsidized tramp steamers from emulating Togo's feat at Port Arthur by being sunk at the entrance to the harbour a line of massive concrete blocks were placed from the shore to the east of Southsea Castle, extending seawards as far as to Horse Sand Fort--one of the three built upon the bottom of the sea. This form of defence was severely criticized, for it proved a source of danger to trading and other private ships, while at high tide a torpedo-boat could with impunity pass over the submerged artificial reef.

Consequently a permanent breakwater, fashioned after the manner of that superb work protecting Plymouth Sound, took the place of the worse than useless concrete blocks; a similar one was constructed from Ryde Sands to the Noman Fort, and thus, with the exception of the main channel between these two hitherto sea-girt forts, Spithead was rendered almost immune from torpedo-boat attacks.

These breakwaters, and indeed all the fortifications on shore, were armed with the latest type of air-craft repelling armament; a three-inch automatic gun, capable of firing one shell per second. The bursting charge of each shell was proved to have an effective radius of a hundred yards, while the creation of air-waves and "pockets" resulting from the detonation, would seriously imperil the stability of every aeroplane within three hundred yards. At night each of these guns was supplied by an ingeniously constructed searchlight that, projecting a narrow ray of light almost parallel with the axis of the gun-barrel, rendered a "miss" an impossibility unless the range was greatly miscalculated. As the sights of the weapon were altered the beam of the searchlight was automatically adjusted. All the gunlayer had to do was to train the searchlight upon the hostile aircraft and fire.

Yet in spite of all these elaborate means of defence the main portion of the British Navy, seemingly anchored in perfect security at Spithead, had received a most unpleasant moral blow. Who and what is this mysterious Captain Restronguet?

CHAPTER II.

SUB-LIEUTENANT HYTHE DISCOVERS THE SUBMARINE.

"Pipe away the diving-party!"

H.M.S. "Ramillies," the flagship of the First Battle Squadron of the Home Fleet, had just anchored in almost the identical position that she had occupied barely a quarter of an hour previously. With mathematical precision the other battleships of the squadron had also returned to their late anchorage and were preparing to investigate the mysterious occurrence in the shape of a complimentary message from the still more mysterious Captain Restronguet.