Le Plongeur

Capt. Bourgeois and M. Brun

Sketch of Le Plongeur (Forward end)

Sketch of Le Plongeur (Aft end)

Length 140 feet 0 inches
Beam 19 feet 6 inches
Displacement 420 tons

In the words of Commander F. W. Lipscomb, ODE, RN:

"In 1858 Captain (later Vice Admiral) Bourgois designed ‘Le project du Plongeur’. This was examined by officers of the Corps of Naval Constructors, and the development was recommended by Brun, a naval Commander and member of the Corps of Constructors (later Director of Naval Construction). The design was accepted and the keel was laid in June 1860. This boat was 140 feet long and displaced 420 tons. The propulsion was by compressed air which drove a propeller. The engine was designed by Brun. The submarine was made of iron plates fastened to a heavy keel which extended right forward to support the spar which carried the explosive charge – an ambitious project.”
"In a hollow part of the hull a salvage boat was fitted, capable of taking twelve men. The boat was bolted to the hull and pressure inside the submarine was kept just above that of the water outside so that there was no seepage of water at the bolts into the vessel.”
"The Plongeur had trouble. She was fitted with a system of moving water from one end of the boat to the other by means of pipes and pistons to control the longitudinal equilibrium. This system worked too slowly so that the boat plunged about. The hydroplanes in the stern were found to have insufficient power to eliminate this so a vertical screw was added. This did not cure the trouble. Besides this difficulty, naval officers considered that the explosive, which was carried on a spar in the bow, was too weak to justify further development of the submarine weapon at that stage. Nevertheless she was the first submarine which did not rely on human power for propulsion. The year was 1863.”1

In the words of Edward Horton:

"She was a remarkable sight, 140 feet long and with a displacement of 420 tons – by far the largest submarine to appear before the twentieth century. The reason for the great size was that the 80-horsepower engine ran on compressed air, and vast quantities of it. Much of Le Plongeur was no more than storage space for enormous bottles of ‘fuel’. Eighty horsepower is not much for a craft of such size, but the main problem centered on underwater stability. The ability to keep a depth line would long plaque submarine designers and crew, but Le Plongeur was particularly erratic in this respect, mainly because she was very long and flat. What happened during trials was that on the surface she behaved well enough, and settled into the awash position unprotestingly after the correct amount of ballast had been added. But when, in order to submerge completely, the final ballast was admitted so as to reduce buoyancy to nothing, ‘zero buoyancy’ as it is called, she surged out of control. Neither horizontal rudders nor an ingenius compressed air device calculated to adjust weight could rectify this. Le Plongeur followed much the pattern of a playful dolphin, but for the crew it was in deadly earnest. She would plummet downwards at a steep angle, and all the correcting gear would immediately swing into action. After a momentary delay she would make a break for the surface, where another ‘correction’ would start the process all over again. For all the technical advances she embodied, Le Plongeur was a failure, and while the French navy had the sense to realize this they did not have the enterprise to build on what was a very real foundation. They abandoned the idea altogether.”2
  1. Lipscomb, Cmdr. F. W., "Historic Submarines", Hugh Evelyn Limited, London, 1970. Pages 17-18.
  2. Horton, Edward, "History of the Submarine", Doubleday & Company, Inc. Garden City, NY, 1974. Pages 30-31.

Gary W. McCue