Immersion was accomplished by the introduction of water into three reservoirs, placed one forward, one aft, and one centre. The water was expelled either by means of compressed air or by a rotary pump worked by an electro-motor. Two horizontal rudders steered the boat in the vertical plane and an ordinary rudder steered in the horizontal.
The Gymnote had her first trial on September 4, 1888, and the Paris Temps described the result in the following enthusiastic language:
She steered like a fish both as regards direction and depth; she mastered the desired depth with ease and exactness; at full power she attained the anticipated speed of from nine to ten knots; the lighting was excellent, there was no difficulty about heating. It was a strange sight to see the vessel skimming along the top of the water, suddenly give a downward plunge with its snout, and disappear with a shark-like wriggle of its stern, only to come up again at a distance out and in an unlooked-for direction. A few small matters connected with the accumulators had to be seen to, but they did not take a month.
Following along the same lines as this boat another boat, considerably larger, was built. Before it was completed, M. Zédé died and it was decided to name the new boat in his honour. The Gustave Zédé was launched at Toulon on June 1, 1893; she was 159 feet in length, beam 12 feet 4 inches, and had a total displacement of 266 tons. Her shell was of "Roma" bronze, a non-magnetic metal, and one that could not be attacked by sea water.
The motive power was furnished by two independent electro-motors of 360 horse-power each and fed by accumulators. In order to endow the boat with a wide radius of action a storage battery was provided.
The successive crews of the Gustave Zédé suffered much from the poisonous fumes of the accumulators, and during the earlier trials all the men on board were ill.
In the bows was a torpedo tube, and an arrangement was used whereby the water that entered the tube after the discharge of the torpedo was forced out by compressed air. Three Whitehead torpedoes were carried. In spite of the fact that a horizontal rudder placed at the stern had not proved serviceable on the Gymnote, such a rudder was fitted in the Gustave Zédé. With this rudder she usually plunged at an angle of about 5°, but on several occasions she behaved in a very erratic fashion, seesawing up and down, and once when the Committee of Experts were on board, she proved so capricious, going down at an angle of 30°-35°, often throwing the poor gentlemen on to the floor, that it was decided to fix a system of six rudders, three on each side.
Four water tanks were carried, one at each end and two in the middle, and the water was expelled by four pumps worked by a little electro-motor; these pumps also furnished the air necessary for the crew and for the discharge of the torpedoes. For underwater vision, an optical tube and a periscope had been provided.
On July 5, 1899, still another submarine boat was launched for the French Navy. She was called the Morse. She was 118 feet long, 9 feet beam, displaced 146 tons, and was likewise made of "Roma" bronze. The motive power was electricity and in many other respects she was very similar to the Gustave Zédé, embodying, however, a number of improvements. M. Calmette, who accompanied the French Minister of War on the trial trip of the Morse, described his experience in the Paris Figaro as follows:
General André, Dr. Vincent, a naval doctor, and I entered the submarine boat Morse through the narrow opening in the upper surface of the boat. Our excursion was to begin immediately; in two hours we came to the surface of the water again three miles to the north to rejoin the Narval. Turning to the crew, every man of which was at his post, the commandant gave his orders, dwelling with emphasis on each word. A sailor repeated his orders one by one, and all was silent. The Morse had already started on its mysterious voyage, but was skimming along the surface until outside the port in order to avoid the numerous craft in the Arsenal. To say that at this moment, which I had so keenly anticipated, I did not have the tremor which comes from contact with the unknown would be beside the truth. On the other hand, calm and imperturbable, but keenly curious as to this novel form of navigation, General André had already taken his place near the commandant on a folding seat. There were no chairs in this long tube in which we were imprisoned. Everything was arranged for the crew alone, with an eye to serious action. Moreover, the Minister of War was too tall to stand upright beneath the iron ceiling, and in any case it would be impossible to walk about.