French submarine Gymnote (Q1)

The boat was designed to operate underwater with a small positive buoyancy, so that without power and rudders driving it downwards it would tend to float to the surface. There were three ballast tanks, one in the centre and one either end. water could be ejected either using compressed air or electrical pumps. Continuous adjustment was needed during a dive. It was originally equipped only with a stern rudder, which gave poor control. At speeds greater than 6 knots (11 km/h; 6.9 mph) the boat would become unstable. At this speed the boat would be angled down 3-5° to maintain depth, so that the bow would be 1.5 metres (4.9 ft) lower than the stern. Further rudders were added at the centre of the boat in 1893, which as well as improving stability meant that she remained more level as it dived.[2]

The original sixteen pole electric motor was designed by Captain Krebs to develop 55 horsepower (41 kW) at 200V and 200A. Gustave Zédé asked Krebs to connect directly the motor to the propeller at 200 rpm. It is the reason why the rotor was 1 metre in diameter and weighed 2 tonnes.[3] The motor was constructed and tested at the Societe des Forges et Chantiers at Le Havre. It was fitted with two sets of brushes, one for forward and one reverse motion. Once installed it was found that the rear bearing was inaccessible and could not be repaired with the motor installed. It was difficult to inspect the armature or repair damage to the insulation. The motor was not designed to come to an immediate halt when power was disconnected, but instead would freewheel to a halt relatively slowly. Reverse power could not be applied until it had stopped moving, so it was not possible to immediately reverse the propeller in case of emergency. The motor proved so problematic that it was replaced with a smaller but more powerful Sautter-Harlé motor.[2]

The boat was originally fitted with 564 Commelin-Bailhache-Desmazures alkaline cells[4] designed from the Lalande-Chaperon patent which used Zinc and copper oxide electrodes with potassium hydroxide electrolyte. These were located all over the ship arranged into six banks of 45 parallel paired cells connected in series. To vary the speed, banks could be connected in different combinations, 6 banks in series giving 150 V and 8 knots, 3 banks in series in parallel with the other 3 in series giving 114 V and 7 knots, 2 banks in series paralleled 3 times giving 84 V and 5.5 knots, all 6 banks in parallel giving 45 V and 6 knots. A bank was capable of delivering a maximum of 166 amps.[5] The whole array weighed eleven tons. A new battery was installed in 1891 using a Laurent-Cely sulphuric acid design having 205 individual 30 kg assemblies of five plates each. Again these were arranged into six banks, now each having 17 parallel pairs of batteries connected in series. At 8 knots (15 km/h; 9.2 mph) range was 32 miles (51 km), at 4 knots (7.4 km/h; 4.6 mph), 100 miles (160 km). Another battery was installed in 1897.[2]

The hull was made of 6 mm steel at the centre, tapering to 4 mm at either end with a circular cross section. Internally it was coated with coal tar to provide protection from spilled battery acid. The hull was supported by 31 circular frames with additional longitudinal bracing.[2]

The boat was fitted with several types of periscopes, but they proved unsatisfactory. Diving was delayed by the need to fix or stow the periscope and water seals proved to be unreliable and on a couple of occasions led to dangerous flooding. A small conning tower was added in 1898. The boat had a compass and a gyroscope. Although the latter were not entirely reliable it allowed the Gymnote to force a naval block in 1890. The ship was equipped with two 14-inch torpedo tubes.[2]