The _Ma Robert_ is said to have been the first steel steamer ever built; she was constructed by Laird’s for the Livingstone expedition to the Zambesi. High tensile steel was used with a limit of elasticity of about twenty-three tons, which is very similar to the metal used in the _Mauretania_ and _Lusitania_ where stresses are to be met. Strength and lightness were essential in the _Ma Robert_ and therefore the new material was used. The little vessel was 73 feet long, 8 feet wide, and 3 feet deep, and was flat-bottomed and of very little draft. But the hull corroded badly and leaked very much, and the steamer came to grief on a sandbank in the Zambesi. The _Rainbow_, built of steel plates in 1858, was a smart, handsome paddle-boat, schooner-rigged, and carrying two very tall masts. She had a high-pressure engine and her steam-pipe emitted the energetic snort which was peculiar to the locomotive of the time. Indeed her high-pressure machinery made such a noise that she could be heard from one side of the Mersey to the other. She was intended for the Niger Exploration expedition, and on her trial attained a speed of between twelve and thirteen miles an hour. She was 130 feet long by 16 feet beam. Although her plates were only one-eighth of an inch thick she had the stiffness and rigidity of a strong ship, and there was almost an entire absence of vibration from the engines. Her boilers, which were of puddled steel plates, were proved up to 200 lb. on the square inch, though they were only worked at 50 to 60 lb. The engine was of 60 nominal horse-power, working up to 200 indicated. The hull was divided athwartship and longitudinally by bulkheads into ten or twelve water-tight compartments. It must be remembered that these experimental steel boats were intended for inland navigation, and being taken to Africa were withdrawn from the observation of practically every one who was competent to judge of the relative merits of iron and steel. Certainly no one attempted to build a steel boat for the ocean for some years afterwards, and it was not until 1875, when the Admiralty, acting upon observations made in the dockyards of France where steel was being used, represented to British manufacturers the importance of improving the quality of steel, that the Siemens-Martin process was brought out, and in consequence two cruisers were constructed of steel produced in this way. [Illustration: THE “BRITANNIC” (WHITE STAR LINE, 1874).] [Illustration: THE “UMBRIA” AND “ETRURIA” (CUNARD).]