Two important features were specified for all: the machinery was required to be wholly below the water-line, and the screw had to be unshippable. Engines were now required for Block Ships and for sea-going vessels. So the principal engineers of the country were called together and were asked to produce engines in accordance with the bare requirements given them. A variety of designs resulted. From the experience obtained with this machinery two important conclusions were quickly drawn: firstly, that gearing might be altogether dispensed with; secondly, that no complex contrivance was necessary for altering the pitch to enable engines to work advantageously under varying conditions, the efficiency of the screw varying very little whether part of the ship’s velocity were due to sail power or whether it were wholly due to the screw.[158] And here it may not be amiss to note, in relation to a nation’s fighting power, the significant position assumed by naval material. In land warfare a rude measure of force could always be obtained by a mere counting of heads. At sea man was in future to act, almost entirely, through the medium of the machine. However we may have deserved the eulogy of the French writer in respect of developing the paddlewheel war steamer, the development of screw propulsion in the next decade was marked by a succession of failures and a large outlay of money on useless conversions and on new construction of poor fighting value, most of which could have been avoided. Had our methods been less tentative and more truly scientific the gain would have been undoubtedly very great; we should have laid our plans on a firmer basis and arrived at our end, full screw power, by a far less circuitous route than that actually taken. In this respect France had the advantage of us.