Such at least is a combined expedition in logical analysis. But so essentially is it a single organism, that in practice these various elements can seldom be kept sharply distinct. They may be interwoven in the most intricate manner. Indeed to a greater or less extent each will always have to discharge some of the functions of the others. Thus the covering squadron may not only be indistinguishable from the escort and support, but it will often provide the greater part of the landing flotilla and even a portion of the landing force. Similarly, the escort may also serve as transport, and provide in part not only the supporting force, but also the landing flotilla. The fourfold constitution is therefore in a great measure theoretical. Still its use is not merely that it serves to define the varied functions which the fleet will have to discharge. As we proceed it will be seen to have a practical strategical value. From a naval point of view it is the covering squadron which calls first for consideration, because of the emphasis with which its necessity marks not only the distinction between the conduct of combined expeditions and the conduct of commercial convoys, but also the fact that such expeditions are actually a combined force, and not merely an army escorted by a fleet. In our system of commerce protection the covering squadron had no place. The battle-fleet, as we have seen, was employed in holding definite terminal areas, and had no organic connection with the convoys. The convoys had no further protection than their own escort and the reinforcements that met them as they approached the terminal areas. But where a convoy of transports forming part of a combined expedition was destined for an enemy's country and would have to overcome resistance by true combined operations, a covering battle-squadron was always provided. In the case of distant objectives it might be that the covering squadron was not attached till the whole expedition assembled in the theatre of operations; during transit to that theatre the transports might have commerce protection escort only. But once the operations began from the point of concentration, a covering squadron was always in touch.