Premature explosions, involving loss of life amongst the gun-crew, the wrecking of the gun itself, not to mention resultant immunity from dismemberment of those previously destined to be the recipients of this unique form of greeting, are _primâ facie_ contingencies to be guarded against; thus, owing to the sudden stresses to which a shell is subjected on the firing of the propellent charge whereby inertia becomes transmuted into velocity both forward and rotary, the steel of which the shell is made must be of such tensile strength that not only will the base-end withstand this transmutation, but the walls of the shell must be capable of overcoming the inertia of the front end of the shell, otherwise they will collapse, and a "premature" will be the immediate outcome. An output of steel adequate for all munition purposes was already a problem sufficiently acute, and there were genuinely orthodox reasons why the home output, in particular, should be maintained at as high a level as possible. For one thing, it was eminently desirable that America should keep supplied our Allies who were less well equipped in "industrial and engineering resources than ourselves." "By home manufacture," too, "we had saved in the course of a single year something which is equal to 6_d._ or 7_d._ in the pound of income tax in the metal market alone." Besides "when you order a very considerable quantity of war material abroad, there is always a difficulty which arises with regard to the exchanges and the gold supply." There was also "the difficulty that you have not the same control over the manufacturers of material abroad as you have got here" [Mr. Lloyd George, House of Commons, December 20th, 1915]. Influenced by considerations such as these, Mr. Cooke undertook not merely to machine _in toto_ a given quantity per month of rough shell forgings, but proffered the extensive steel-making plant in Crewe Works, comprising several furnaces of 20 and 30-ton capacity, both for the supply of steel requisite for the initial manufacture of these rough forgings, and if desired, for a further output of steel wherewith to supply forgings to other firms engaged exclusively in shell manufacture.