Recent inventions in modes of aërial transportation and communication, notably by means of the aëroplane, dirigible balloons, and radio or wireless telegraphy, make it seem necessary (or at least desirable) to deal separately with aërial warfare.
437. Few Positive Rules of Aërial Warfare. -- Very few positive rules or principles of International Law applicable to this field of future warfare have been thus far developed. The rules are largely inferential and speculative in their character, and are based upon generally recognized principles or analogous practices in land or naval warfare.
438. The Hague Declaration. -- Many of the States represented at the Second Hague Peace Conference of 1907 agreed to "prohibit, for a period extending to the close of the Third Peace Conference, the discharge of projectiles and explosives from balloons or by other new methods of a similar nature."2 But this "Declaration" was only signed by twenty-seven States, and the Signatories did not include four of the great maritime Powers.3 It cannot, therefore, be regarded as an integral part of International Law and was not in force during the World War.
439. The Hague Regulations. (a) As to Bombardment. -- The only positive rule of International Law bearing directly on the subject of aërial warfare which is based upon convention is found in the Hague Regulations respecting the Laws and Customs of War on Land:
"The attack or bombardment, by any means whatever,____________________