This use might be well subdivided into legitimate and illegitimate offensive operations. There has been, unfortunately, ample example of the use of both airships and aëroplanes for purposes that are illegitimate and barbaric in the present war. To use the advantage of travelling in the air at altitudes for the purpose of the wanton destruction of harmless citizens, and, further, to destroy in cities the amassed wealth of art that only centuries, not years, produce, is an unrighteous use of the science of aërial navigation. Before the war it was condemned by the Hague Convention. Since, it has met with the denouncement of all civilised nations--save the one that has perpetrated the outrages. In the case of the aëroplane raid made into Germany by our own British naval airmen, one party of aviators went to Cologne to try to attack the airship halls there. The city was enveloped with an opaque fog, and it was hopeless to try to locate the position of the airship sheds. Though the British aviators circled over the town for an hour and a half they refrained from discharging any bombs, rather than run the risk of destroying civilian life or property. An example, indeed, of the legitimate offensive use of the aëroplane was the attempt to destroy or put out of action the very kind of aircraft which had been so wantonly used over Paris, Antwerp, Ostend, and other cities. Perhaps the most important offensive use of the aëroplane is for fighting airship and aëroplane. Mention has already been made about the deadly character of the aëroplane when it encounters an airship. When it meets an aëroplane the chances are more evenly balanced. Success will depend chiefly upon the speed of the respective aëroplanes, their climbing power, their armouring, and the guns with which they are armed. Speed and climbing power are perhaps the greatest protective factors. Several stories have already been told of the pursuit of German aëroplanes by those of the Allies. The climbing power of the machines of the latter has often been the cause of victory. It is the well-directed shot from above to which the airman is exposed that has ended the career of airman and machine. At the beginning of the present chapter it was pointed out that the British and French aëroplanes generally fly at about 6,000 feet, which is a height fairly safe from gun-fire. While speaking of the offensive work of aëroplanes, a few more words about the attack on them by gun-fire may not be out of place. As Mr. Lanchester has pointed out, an aëroplane is liable to attack by rifle, machine-gun, and shell fire. Ordinary field artillery fire can be put out of the question in the use of so rapidly moving a target as an aëroplane in flight. He has estimated that an aëroplane is absolutely safe from rifle or small-bore machine-gun fire at 7,000 feet, and it would be difficult to hit it a thousand feet lower.