Though it is difficult to foretell on what lines aircraft will develop for any one purpose, as in the past, the problem of military co-operation will perhaps be less complex than that of co-operation with the Navy. It will probably consist of improvements along the lines already indicated, such as increased range, speed, climb, man[oe]uvrability, offensive armament, armour, the assistance of tank and anti-tank action, and the utilization of gas. Fighting will undoubtedly take place at very high altitudes to keep the enemy's fighting machines away from the zone of operations--necessitating the development of the single-seater so as to increase climb and man[oe]uvrability, and obtain, if possible, a speed of 200 miles an hour at 30,000 feet. Cavalry, unless retained, as I think they should be, in the form of mounted machine-gunners, will, I think, disappear in European warfare, but infantry will remain, and it will be the object of aircraft to assist their advance by reconnaissance, ground attack, artillery and tank co-operation, and the destruction of the enemy's supplies and communications. In this connection ground tactics and air tactics must develop _pari passu_ and commanders of Corps and Armies must work out during peace training the fullest schemes for the most intimate co-operation between air and land forces. The future of naval co-operation is a difficult problem, more especially as there was no major naval engagement after Jutland in which aircraft could be used, and consequently we have little to go on in estimating their practical value in direct co-operation with the fleet. It is impossible at present to judge between the conflicting opinions as to the future of the capital ship, but it is certain that aviation will materially modify naval tactics and construction. Coast defence, reconnaissance, anti-submarine work, escort, and the bombing of enemy bases, will doubtless continue and develop with ever-increasing machinery and equipment; but torpedo attack by aircraft may reach a point where the very existence of opposing fleets may be endangered. It is already questionable whether a battleship could survive an attack launched by even a small force of this mobile arm. As was the case during the war, the action of aircraft at sea is restricted by range, the difficulty being to find the mean between the opposing conditions of radius of flight and limitation in the size of aircraft imposed by the deck-space of "carriers," but there is reason to suppose that on the one hand engines will be so improved as to afford a sufficient radius of action to comparatively small aircraft, while, on the other, devices will be found to economize deck-space.