It is evident that the designer of this vessel miscalculated and made his boat so much overweight that she could not be given sufficient buoyancy to bring her to the surface by the means provided. From a study of the form of this vessel, she should have been very stable, and I am of the opinion that she could have been successfully navigated submerged had she been properly ballasted. [Illustration: THE "INTELLIGENT WHALE" Built by O. S. Halstead of Newark, N. J., and sold to the U. S. Government in 1870, now in Brooklyn Navy Yard.] During the years 1863 and 1864, Messrs. Bourgois and Brun brought out for the French Navy the largest and, in some respects, the most completely equipped submarine that was produced during the nineteenth century. This was _Le Plongeur_, a vessel about one hundred and forty feet long, ten feet depth, and twenty feet beam, with a displacement of over four hundred tons. Her motive power consisted of compressed-air engines of eighty horsepower. The compressed air was carried in air tanks at a pressure of one hundred and eighty pounds per square inch. It is reported that the capacity of the air tanks exceeded one hundred and forty cubic metres. [Illustration: LONGITUDINAL SECTION OF THE FRENCH SUBMARINE "LE PLONGEUR" This vessel was built by Messrs. Bourgois and Brun in 1864 and was backed by the French Government. She was the largest and the most costly vessel built in the attempt to solve the problem of successful submarine navigation up to about the beginning of the 20th century. (See text.)] Her submerged control system consisted of the usual water-ballast tanks for reducing the vessel's surface buoyancy preparatory to submerging. The final adjustment of displacement was to be effected by means of cylinders which could be forced out through stuffing boxes to increase her displacement or withdrawn to reduce her displacement. It was hoped that by manipulating these cylinders she could be put in equilibrium with the water she displaced, and that she could then be steered in any desired direction by the vertical and horizontal rudders placed at her stern.