Accordingly a sufficient length of stout rope was lashed round one of the floats and also to the lorry. At the signal the powerful vehicle began to move slowly ahead, and, with hardly a hitch, the float slithered over the sand up the incline and on to the hard ground. The second float followed suit, and then came the task of loading up. By the time the two floats, the dinghy, and the gear were piled upon the lorry there was precious little room for eleven persons, but the Royal Air Force men were not to be deterred by trifles. Swarming all over the small mountain of gear, and even perched upon the canvas awning, they returned tired but triumphant. At last the work of salvage was completed, although the actual amount of material recovered was but a moiety of the original sea-plane. Upon entering the ante-room of the mess Derek and Kaye encountered Grainger, lieutenant and hydro expert. Grainger was in high spirits. His particular task was to get a hydro-glisseur into running order before he proceeded on Christmas leave, and in spite of numerous difficulties he had achieved his end. "The priceless old thing has been running this morning," he declared. "I'm taking her for a spin up to Fisherton. Coming, you fellows?" "Right-o!" replied Derek. "Hang on half a minute until I change my socks and sea-boots. I'm carrying about a quart of sea water in each boot, and it's beginning to feel slightly damp." The hydro-glisseur, as its name implies, is a weird sort of craft that skims on the surface of the water and is propelled by a two-bladed aerial propeller. The body consists of six floats lashed together in pairs. Credited with a speed of fifty knots, hydro-glisseurs are used for towing aeroplane targets at high speed, while air-craft hovering overhead try their level best to bomb the targets into fragments. "You'll want your flying-kit, you fellows," declared Grainger, as the trio prepared for the trial trip. "Unless you want to be as deaf as posts, don't forget your helmets." Arrayed in leather jackets, flying head-dress and fur-lined gloves--gear that took Derek's thoughts back to those seemingly far-off days at Torringham aerodrome and on the Western Front--the "glisseurs" made their way to the boat-sheds out of which the freak craft were moored. A few minor adjustments, and the powerful engine fired. Throttled well down, the motor was running at sufficient speed to make the propeller buzz as it cleft the air. "All ready? Let go!" roared Grainger. A touch of the controls, and the glisseur gathered way. Soon she began to lift under the enormously powerful drive of the huge propeller, until, with a deafening roar that could be heard for miles, the freak craft quickly worked up to a speed of certainly not less than forty-five knots. Presently Grainger throttled down. "There's a Boche submarine alongside Fisherton Quay," he announced. "She came into harbour at lunch-time. I vote we go and have a look at her."