The Evolution of Naval Armament

by Frederick Leslie Robertson

But in spite of all prepossessions against it the screw had won a decisive victory over its rival. So striking were the results recorded by the Archimedes, that a decision was made in December, 1840, to change the Great Britain, an Atlantic liner then under construction, from paddlewheel to screw propulsion. In two ways she was a gigantic experiment: she was the first large ship to be built of iron, and it was now proposed to fit her with a screw. Mr. Brunel took all the responsibility for advising the adoption of both these revolutionary features; the result was a splendid testimony to his scientific judgment, boldness of enterprise, and “confident reliance on deductions from facts ascertained on a small scale.”

Before the completion of the Great Britain the Admiralty had initiated experiments which were to furnish important information as to the power and efficiency of the screw propeller in its various forms, and to settle beyond cavil the question of its superiority over the paddlewheel for the propulsion of warships. The sloop Rattler, 888 tons and 200 horsepower, was fitted with screw machinery. Several forms of screw were tried during the winter of 1843–4. First the screw as used in the Archimedes was fitted: a screw of 9-foot diameter, 11-foot pitch, and of 5½ feet length, consisting of two half-convolutions of a blade upon its axis. Then a screw was tried of the same diameter and pitch but of only 4-foot length; and then the length was again reduced to 3 feet. The effect of cutting down the length was to give an increase of efficiency.[156] The screw was again shortened by 2 feet, and finally to 1 foot 3 inches; with each reduction in length the slip diminished and the propulsive efficiency increased. Various other forms of screws were tried, and it was shown that Pettit Smith’s short two-bladed propeller was on the whole the most efficient.

The best form of screw having been determined, it still remained to compare the screw propeller with the paddlewheel. Accordingly the Alecto, a paddlewheel sloop of similar lines to the Rattler, was selected as the protagonist of the older form of propulsion, while the Rattler herself represented the screw. Naval opinion was still completely divided on the great question, while in the competing sloops the utmost emulation existed, each captain advocating his own type of propeller. The speed trials took place, and showed the Rattler to have an undoubted advantage. The paddlewheel, however, laid claim to a superiority in towing power. So a further competition was ordered, as realistic as any, perhaps, in the history of applied science: nothing less than a tug-of-war between Paddle and Screw, those two contending forms of steam propulsion! Lashed stern to stern and both steaming ahead full power, one evening in the spring of ’45 the two steamers struggled for mastery. And as Rattler slowly but surely pulled over Alecto, the question which had been for years so hotly debated was settled; the superiority of the screw was demonstrated. With the adoption of the screw the problem of disposing the armament was settled. The broadsides and the spaces between decks were once more free to the guns along the entire length; moreover the action of the screw was in complete harmony with that of the sails. With the screw as an auxiliary to sail power, and subsequently with the screw as sole means of propulsion, a change came over the character of the pivot armament. Whereas with the paddlewheel the pivot gun was the chief means of offence, when the screw was introduced the broadside was restored, and though the heavy pivot guns were retained (steam and the pivot gun had become associated ideas), yet by their comparatively limited numbers they became a subordinate element in the total armament.

RATTLER VERSUS ALECTO

From an aquatint in the South Kensington Museum

External affairs now lent a spur to screw propulsion. In ’44 the French navy came under the reforming power of the ambitious Prince de Joinville, and from this year onwards the attitude of France to this country became increasingly hostile and menacing. The thoughts of the French were turned toward their navy. No sooner had de Joinville been placed in command than schemes of invasion were bruited in this country; and the public viewed with some alarm the altered problems of defence imposed on our fleets by the presence in the enemy’s ports of a steam-propelled navy. Sanguine French patriots sought to profit by the advent of the new power. A pamphlet appeared in Paris claiming to prove that the establishment of steam navigation afforded France the very means by which she could regain her former level of naval strength. The writer, using the same arguments as Colonel Paixhans had used in ’22, reviewed the effect of steam power on the rival navies, and pointed to the Duke of Wellington’s warnings in parliament of the defencelessness of the English coasts and to his statement that if Napoleon had possessed steam power he would have achieved invasion. These cries of alarm, said the writer, should trace for France her line of policy. She should emulate the wise development of steam propulsion as practised by Great Britain. “We think, England acts; we discuss theories, she pursues application. She creates with activity a redoubtable steam force and reduces the number of her sailing ships, whose impotence she recognizes.... Sailing vessels have lost their main power; the employment of steamers has reduced them to the subaltern position of the siege artillery in a land army.” The writer praised English policy in the matter of steam development: its wise caution, its reasoned continuity. There had admittedly been some costly deceptions. Nevertheless the method was to be commended, and France should proceed in a similar manner: by a succession of sample units while steam was still in the experimental stage, by far-sighted single strides, and then by bold and rapid construction of a steam navy which would compete on more even terms with that of her hereditary rival.[157]

Faced with the probability that our rivals would pursue some such progressive and challenging policy as outlined by the pamphleteer, the Admiralty acted rapidly. Before the Rattler trials were complete a decision was made favourable to the screw propeller, and an order was made for its wide application to warships built and building. It was resolved, on the advice of Sir Charles Napier, that the screw should be regarded solely as an auxiliary to, and in no way as in competition with, sail power. The Arrogant was laid down, the first frigate built for auxiliary steam power; and screws driven by engines of small horse-power were subsequently fitted to other ships with varying degrees of success.

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.