Under the direction of the Air Department much attention was paid by pilots in the Naval Air Service to experimental work and the diverse uses of aeroplanes. So early as January 1912 Lieutenant H. A. Williamson, R.N., a submarine officer who had gained the Royal Aero Club certificate, submitted to the Admiralty a paper which anticipated some later successes. He advocated the use of aeroplanes operating from a parent ship for the detection of submarines, and showed how bombs exploding twenty feet below the surface might be used to destroy these craft. The practical introduction of depth charges was delayed for years by the difficulty of devising the delicate and accurate mechanism which uses the pressure of the water to explode the bomb at a given depth. But before the war ended the detection of submarines from the air and the use by surface craft of depth charges for destroying them had been brought to such a degree of efficiency that the submarine menace was countered and held. The submarine learned to fear aircraft as the birds of the thicket fear the hawk. It would be tedious to attempt to describe the long series of experiments by which this result was at last attained. The earliest attempts to detect submarines from the air were made with seaplanes at Harwich in June 1912, and at Rosyth in September of the same year. The shallow tidal waters were found to be very opaque, but in clear weather a periscope could be seen from a considerable distance, and in misty weather the seaplane, when it sighted a submarine in diving trim on the surface, could swoop down and drop a bomb before the submarine could dive. Progress in bomb-dropping was not less. Nothing is easier than to drop a detonating bomb, with good intentions, over the side of an aeroplane; the difficulty of hitting the mark lay in determining the flight of the bomb and in devising an efficient dropping gear. To drop a weight from a rapidly moving aeroplane so that it shall hit a particular spot on the surface of the earth is not an easy affair; the pace and direction of the machine, its height from the ground, the shape and air resistance of the bomb, must all be accurately known. They cannot be calculated in the air; success in bomb-dropping depends on the designing of a gear for dropping and sighting which shall perform these calculations automatically. Very early in the history of aviation dummy bombs had been dropped, for spectacular purposes, at targets marked on the ground. The designing of an efficient dropping gear and the study of the flight of bombs were taken up by the Air Department of the Admiralty from the very first. Under their direction a very valuable series of experiments was carried out at Eastchurch, at first by Commander Samson, and later by Lieutenant R. H. Clark Hall, a naval gunnery lieutenant, who had learnt to fly, and was appointed in March 1913 for armament duties with the Royal Naval Air Service.