The first application of steam for the purpose of towing vessels—now an important and invaluable part of the numerous services rendered by steam to navigation—was made in October 1816, when the _Harlequin_ was towed out of the Mersey by the _Charlotte_, a steamer which, in the summer of the same year, had been placed as a ferry-boat to run between Liverpool and Eastham. But the first steamer specially built at Liverpool for the purpose of a ferry was named the _Etna_, which, early in April of that year, began to ply between Liverpool and Tranmere. She was 63 feet long, with a paddle-wheel placed in the centre, her extremities being connected by beams, and her deck 28 feet wide over all. This primitive vessel initiated the mode of transit by means of the ferry-boats which now bridge the Mersey. [Sidenote: H.M. steam-ship _Comet_, 1819.] It was not, however, till the year 1819 that the Admiralty of the day became alive to the importance of steam navigation, nor were they likely, even then, to have awakened from their slumbers had not Lord Melville and Sir George Cockburn urged on the Government the great value of steam-power for towing their men-of-war.[107] In that year the first steam-vessel was built for the Royal Navy. She was named the _Comet_, and her dimensions were 115 feet in length, 21 feet in breadth, and 9 feet draught of water, being propelled by two engines of 40 horse-power each, manufactured by Boulton and Watt. [Sidenote: The _Rob Roy_ and other vessels, 1818.] In 1818, Mr. David Napier, a name more associated than any other in Great Britain with the early development of the marine engine, having for some years previously been giving his attention to the propulsion of vessels by steam, launched the _Rob Roy_ from the yard of Mr. William Denny, of Dumbarton.[108] She was only 90 tons burthen, with engines of 30 horse-power, but, to the credit of her builder, she traded between Glasgow and Belfast, carrying with great punctuality the mails and passengers for two consecutive years without requiring any repairs; and although the first regular sea-going steamer which had been built in either Europe or the United States of America, her success was complete. Subsequently, the _Rob Roy_ was transferred to the English Channel to serve as a packet between Dover and Calais. Soon afterwards Messrs. Wood, of Port Glasgow, built for Mr. David Napier, who had by this time removed to London, a boat named the _Talbot_, of 120 tons. She was fitted with two engines of 30 horse-power each, of his own construction, and proved in all respects the most perfect steam-vessel of the period. This was the first vessel placed upon the now celebrated line carrying the mails and passengers between Holyhead and Dublin.