[Illustration: THE OLD “DREADNOUGHT.” _Photograph by E. Sankey, Barrow._] [Illustration: THE BIG GUNS OF THE OLD “DREADNOUGHT.” _Photograph by E. Sankey, Barrow._] The _Thunderer_, a sister ship in some respects to the _Devastation_, and the _Fury_, afterwards called the _Dreadnought_, followed, but each one included improvements and modifications suggested by the experience gained with the _Devastation_. Hydraulic machinery was installed for working the 38-ton guns of the Woolwich rifle pattern, but in the _Thunderer_ the two 35-tons were worked by hand. Their guns were by no means generally approved, many artillerists being of opinion that Whitworth hexagonal guns would have been better. The important feature in the _Thunderer_, and one which contributed very materially to her safety, was the introduction of a longitudinal watertight bulkhead between the two sets of engines and boilers, so that if one set should be disabled from any cause, the vessel would still have the other set to depend upon. The _Dreadnought_ was engined on the compound system, which gave her a better speed on a proportionately less coal consumption. It is an old saying that the speed of a fleet is that of its slowest ship. When the situation was further complicated by the varying sailing powers of the ships the difficulty of the admiral in command to keep his fleet together must sometimes have been very great. Admiral Yelverton, for instance, when in command of a Channel squadron, in 1866, consisting of the _Caledonian_, _Lord Clyde_, _Bellerophon_, _Achilles_, _Hector_, _Pallas_, _Ocean_, _Wyvern_, _Research_, and _Helicon_, reported that he “took every opportunity of trying them to their utmost, always placing them in positions as to wind and sea most likely to test their capabilities as sea-boats, without much regard to the safety of their spars or the risk of shipping far more water than under ordinary circumstances ships of war would be exposed to.... “The _Pallas_ and _Research_ were the only two ships that could not keep company with the squadron. The _Pallas_ appeared to plunge heavily, and carried away her jib-boom, but took her place in the squadron on the following morning. The _Research_, from her very small steam power, was out of sight at sunset, and put into Plymouth to fill up with coal. On the 23rd we reached the prescribed rendezvous ... when steaming ceased for a while, and the trials of sailing began.” The ships varied as much under sail as they did under steam. The _Wyvern_, which was not a good sea-boat, and her sister ship, the _Scorpion_, were built for the Confederate States, in 1864, at Birkenhead, and were bought by the British Admiralty. They were 220 feet by 42 feet, and of 1,827 tons, and had engines of 350 nominal h.p. Each had two turrets containing two 300-pounders. They had ram bows, and, except on the poop and forecastle, the bulwarks could be let down when the ships were cleared for action.