This lecture is an attempt to give a brief survey of some facts observed during the German-Polish campaign, which are thought to be of interest to the aircraft industry. The authors wish to stress that they fully realise the scarcity of actual data on which any possible conclusions could be based. There is no doubt that a “Blitzkrieg” provides all of the experience to the winner, particularly if he enjoys an overwhelming superiority in the air and has secured a “total” victory, as was the case in this campaign. His vision was clear and far-reaching, his striking arm able to inflict blows, wherever required by tactical considerations.

Explicitly or implicitly the yield strength of a material is often used as a measure of incipient structural damage. With the yield strength determined by conventional methods, however, it cannot be said in general for two structural elements geometrically alike but of different materials that similar loads, producing maximum stresses equal to the yield strengths in the two cases, are simply related to the yield strengths. A definition of yield strength is proposed in this paper which often has the advantage that, for geometrically similar structures of different materials, loads producing maximum stresses equal to the yield strength are proportional to the yield strength.

Petrol is a highly inflammable fluid which can be ignited easily and whose vapour forms with air a highly explosive mixture.

There are, however, possibilities of giving a certain amount of protection against such fire risks created by damage to petrol tanks.

The three main problems which have to be dealt with are:—

1. (i) To exclude an ignition which may be caused by bullets hitting a petrol tank;

2. (ii) To seal leaks caused by bullet holes;

3. (iii) To prevent fire after a crash.

These problems are by no means new. A large amount of research and experimental work has been devoted to their solution.