Hence the aerial war unit already formed in Germany, and likely to be in existence everywhere else ere another year or so has passed. This unit is a dirigible of great offensive powers, associated with a number of aeroplanes presumably intended to defend it and ward off and defeat attack by hostile aeroplanes. This is merely the crude beginning, it seems reasonably safe to prophecy that in the early future the aerial war-unit will be made up somewhat as follows:-- (_a_) An offensive dirigible, carrying the maximum of bombs, etc. (_b_) One or two dirigibles carrying oil and petrol for the aeroplanes--possibly capable of dealing with all minor repairs and of carrying a certain number of aeroplanes on board. (_c_) A number of war aeroplanes specially designed for fighting other aeroplanes and attacking hostile dirigibles as chances may occur. (_d_) A few very swift one man aeroplanes which will be the eyes of the unit. This seems an early certainty. After all it merely reproduces for the air what centuries of experience have shewn to be essential for fleets and armies. The matter is a fascinating subject for speculation; but in connection with a work that exists merely to deal with things as they are at present, is perhaps, better not now pursued further. One point, however, may perhaps be mentioned, and that is that victory or defeat in aerial warfare seems likely to depend upon which side can first destroy the other's bases. A base-less dirigible will not live long. This is likely to lead to very great attention being paid at an early date to anti-aircraft guns and other devices for the defence of aerial bases. Reverting to the arrangement of the present edition, a few words may be said about some of the changes. As stated last year the clumsy old system of grouping monoplanes, biplanes, etc., separately has been abolished. So many firms specialise in both that any such grouping could only lead to confusion. A tabular system has been generally adopted for most new matter. This will be found far more convenient for reference, and of course, saves a great deal of space. The effective age of aeroplanes is somewhat of a vexed question, for while one year probably represents the really effective war utility endurance, even in peace time, school life is more or less indefinite and so is ordinary private life. Consequently--although "dead machines" are excluded it has not been possible to draw an exactly uniform age limit line beyond that. Speaking generally modern machines represent as a rule detail improvements rather than the complete changes of the past. For example, the gap between 1911 and 1913, is far less than the gap between 1909 and 1911. This fact is beginning to make itself felt in war machines.