Carriers are an expensive way of providing a modest amount of air power. Like all forces, they have limitations. They are more vulnerable than airfields and harder to repair after damage, even if not sunk. Against serious opposition much of their effort goes into defending themselves, and they need a protective entourage. Even then, a single carrier is at severe risk within range of enemy air power (or missiles, or submarines). It cannot give much if any support if the operational theatre is deep inland. Two carriers cannot guarantee, as a basis for political commitment, the timely availability of one in the right place. A distinguished admiral has said that there is a case for three or none, but not two.