Obviously, rate of fire should be one of the last things to be sacrificed; but the alternative—a reduction in the load of ammunition—involves a curtailment of the period of activity, and, as a corollary, an increase in the number of machines required for a given combatant duty. Once admit the necessity for such additional machines, and we must estimate the sacrifice, or price paid for the armour, in terms of the loss of fighting strength due to the absence of a section of the air-fleet occupied in replenishing. This is evidently a serious matter under the best conditions—i.e., when fighting in the immediate vicinity of the base; if, however, an air-fleet be engaged far afield it becomes still more serious, and the sacrifice of rapidity of fire, rather than reserve of ammunition, might well prove to be the lesser of evils.
The foregoing illustration shows that, tangibly or intangibly, the matter is one of figures, or, at the worst, a balance of advantages not capable of ready numerical expression. It may thus not always be possible to lay it down definitely whether in theory given conditions mean the abandonment of armour or otherwise; but nevertheless the fact is determined by the sum of the conditions, and where theory is dumb the decision will require to be taken on actual experience, as in analogous problems in naval construction.
§ 57. Protection by Armour and Shield Contrasted. It is, perhaps, opportune to draw attention here to the difference between shield and armour as a means of protection. The shield is essentially mobile, it is moved round and about to give the best protection possible, according to the direction of attack. A shield commonly forms part of a gun-mounting, but this is by way of being an accidental circumstance; the gun has to be trained on the enemy, and so the shield is made part and parcel of the gun, thus automatically taking the best position
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