No sooner had the shell gun given proofs of its destructive powers than experiments on the penetrative power of projectiles began to assume importance, and as early as 1838 trials were being made at Portsmouth against a hulk, the result of which, confirming the experiments made by the French with the _Pacificateur_ some sixteen years previously, demonstrated the far-reaching effects of explosive shell against a ship’s side-timbers. Four years later the prime minister was apprised from New York that the Americans had discovered a suitable and adequate protection for ships’ sides; iron plates of three-eighths of an inch in thickness, riveted together to form a compound 6-inch plate, were alleged to have been found ball-proof. On receipt of which intelligence the Admiralty instructed Sir Thomas Hastings, captain of the _Excellent_, to confirm or disprove by actual trial. Trial was made, but it was reported that no protection was afforded by such plates against the fire of 8-inch shell or 32-pounder shot, even at 200 yards’ range. No defensive remedy could be devised against shell fire, and the only counter-measures deemed practical were of an offensive nature, viz. to mount shell guns as powerful as those of the enemy, and to keep him at a distance by the employment of large and far-ranging solid-shot ordnance. In the meantime iron, which was not acceptable as a protection, had been accepted as a constructive material for ships. For some years it had been increasingly used for mercantile shipping with satisfactory results. The scarcity of timber and its cost, as well as the positive advantages to be obtained from the use of the much stronger and more plentiful material, had decided the Admiralty in ’43 to build iron warships. Some small vessels were built and, in spite of adverse criticism and alarming prediction, acquitted themselves admirably on service. In ’46 it was resolved, however, to put iron to the test of artillery. An iron steamboat, the _Ruby_, was used as a target by the _Excellent_ gunners, and the results were unfavourable; the stopping power of the thin metal was small, and the balls which went clean through the near side wrought extensive damage on the opposite plates. In ’49 trials were made with stouter plates with more promising results: a report favourable to iron as a protection for topsides was made. But in ’51, as the result of elaborate trials made against a “mock up” of the side of the _Simoon_, the previous conclusions were reversed. Iron was condemned altogether as unsuitable for ships of war. “The shot and shell,” reported Captain Chads, “on striking are shivered into innumerable pieces, passing on as a cloud of langrage with great velocity,” and working great destruction among the crew. Nor was a combination of wood and iron any better. In fact the report claimed that, as regards the suitability or the unsuitability of iron, these experiments might be deemed to set the question at rest. The experience