Between this time and the latter portion of the century innumerable submarine boats were designed and a considerable number of experimental ones actually built. A few of them promised very well, though most were failures, the principal reason of their non-success being the want of a suitable means of propulsion. Every conceivable method was attempted, but it was not till the advent of the internal-combustion engine that the submarine became a really practical proposition. Space forbids mention of even a tithe of these inventions, but among the most notable was that invented by the German Bauer, between 1850 and 1860, when he made a futile attempt to blow up a Danish man-of-war. Then there were the _Davids_, used by the Confederates in the Civil War in America. Most of these drowned their crews. One, however, succeeded in torpedoing the Federal sloop _Housatonic_, but accompanied her to "Davy Jones's locker". A Swede, Mr. Nordenfeldt, built about half a dozen submarines between 1880 and 1890, one for this country, one--his first experimental one--which was eventually purchased by Greece, two for the Turkish Government, and, lastly, two or three for the German Admiralty. All of these may be regarded as experimental craft, but they are noteworthy as being the first submarines to be equipped with Whitehead torpedoes, and certainly marked a step forward in the science of underwater navigation. The French navy was the first to tackle the problem of submarine navigation with any real enthusiasm. French inventors had been responsible for a very large proportion of the designs for submarines, which had continually increased in numbers as the nineteenth century progressed. After extensive experiments with the _Gymnote_ (launched 1888), _Gustave Zèdé_ (1893), and _Morse_ (1899), France set about the construction of a regular submarine flotilla of considerable size, launching nearly thirty boats between 1900 and 1903. Other Powers, except perhaps Russia, held back from the new departure, and it is not impossible that it would have been politic for the British Government to have maintained that attitude, in accordance with the views of Lord St. Vincent, and to have announced that it would refuse to recognize the crews of submarines as legitimate belligerents. To have done this would not have been to enunciate any new theory, for from time immemorial this was the attitude adopted by all navies towards the crews of fire-ships, and that it was later on accepted to apply to those who made use of torpedoes and floating mines is evident by the following quotation from the naval officer's diary which has already been referred to.