The launching gear, unlike a torpedo tube, could not be reloaded when submerged, so many Russian boats carried up to eight torpedoes externally.
From an early stage of submarine development the French, who also used a form of drop collar, well understood the value of hull streamlining to reduce resistance and boost underwater speed. Their drop collars were faired into the casing, or even covered by hinged flaps. The Russians, on the other hand, mounted their drop collars too low, which affected hydrodynamic efficiency on the surface, and cannot have helped the boats when submerged. To remedy this shortcoming, the submarines of the Bars class were progressively rebuilt, the collars being moved initially to the curved deck edge of the hull, and finally on to the deck itself. One major problem still dogged the Russian boats: mounting the torpedoes in external drop collars left them exposed to icing up in the severe conditions of the Russian winter.
THE FRENCH SIMONOT DEVICE
The French have a penchant for being different. They were attracted to the simplicity of the external drop collar but then turned it into a much more sophisticated version. The result was the ‘appareil Simonot’, invented by Ingénieur en chef de 1ère classe Jean Ernest Simonot, who was also responsible for designing the carrier submarines. These were armed with conventional fixed torpedo tubes, but also trainable sets of torpedo tubes as on a surface ship. It appears that French had little trust in gyro angling, and went one further in including a version of the drop collar that was also trainable.
The Simonot device held the torpedo in an external cage, suspended from an overhead rail which could pivot out from the line of the hull on a vertical axle at the rear. A compressed air piston released the clamps holding the cage to the hull, and also acted on the swinging arm, starting it on its traversing arc — which relied also on the water pressure from the forward movement of the boat. The forward Simonot devices on the submarine Diane could swing through a total arc of 165 degrees, from straight ahead to 75 degrees aft of the beam. When the device was oriented in the desired direction, the torpedo motor was started and it exited the cage. It was to be hoped that the modest forward underwater speed of the boat did not have an influence on the course taken by the torpedo. The French fitted this complicated device to several of their submarines of the Great War period, later removing them from the aft position where they relied instead on traversing torpedo tube mounts, but the forward fittings remained in use until the boats were withdrawn from service in the 1930s. One must assume that, given the effort expended on their conception and manufacture, the French were determined to hang onto them for as long as possible.
BROADSIDE AND TRAVERSING TUBES
Some First World War British submarines, beginning with E 11, had broadside torpedo tubes for 18in torpedoes — a curious arrangement, wasteful of space, and difficult to aim compared with bow and stern tubes, requiring the boat to slow or stop and fire with gyro settings. The torpedo tubes were of the same split tube pattern as used in the submerged torpedo flats of battleships and cruisers of the era, as there was no space behind the tubes in the narrow confines of the submarine hull to load via a rear door. The tubes also pierced the inner pressure hull, weakening the whole structure, and took up space used by the external ballast tanks. Given the small size of the boats, however, it was one way to drastically increase the torpedo armament.
The steam-powered ‘K’ class were originally conceived as ‘submersible destroyers’. They were provided with a large midships torpedo flat. As well as their four 18in bow tubes, the Ks had four broadside tubes firing two to each beam, plus spare torpedoes hung overhead or stowed between the tubes. In addition, as befitted their high speed surface role of accompanying the battle fleet, the ‘K’-class boats were originally designed to carry a training twin-tube mounting on deck, ‘for night actions’, the submerged tubes being employed for ambushing damaged units of the High Seas Fleet limping home. But the training twin mount had to be removed as it was too exposed to damage in high seas on the low freeboard deck of the ‘K’ boats.
Some French designs of the Great War era carried internal tubes, external Simonot devices and an external traversing multiple mounting. This must have posed significant tactical problems and was one over-complication too many. French submarines built in the 1930s typically had one eternal training mount aft of the conning tower, and another traversing mount at the rear extremity of the casing.
They were a means of carrying additional tubes, external to the pressure hull, for a larger torpedo armament than normal, while retaining the streamlined lines of the hull. In comparison, British boats of the ‘T’ class mounted external tubes but as excrescences, which must have detracted from underwater performance and could even have generated additional noise. Naturally, any and all external tubes suffered from the disadvantage of exposing the torpedoes outside the pressure hull, making maintenance difficult, if not impossible, and obviously the tubes could not be reloaded at sea. Finally, some designers felt that having torpedoes carried externally posed an extra hazard when under depth-charge attack.
When Ateliers et Chantiers de la Loire built the diminutive boats Ronis and Spidola for the Latvian navy, they were fitted with six 18in torpedo tubes, two in the bows and four in two twin training mountings, one fore and one aft. The three boats of the Wilk class from the same builders, supplied to Poland, had a similar arrangement but with 21in torpedoes.
An additional French speciality was the introduction of a smaller torpedo, of 400mm diameter (15.75in), specifically for sinking merchant ships, leaving the heavier 21in torpedoes for attacks on warships. This was a strange development, as the small 400mm torpedoes might disable a large merchantman, but could not be guaranteed to ensure sinking it quickly. Very few merchant ships, other than tankers, were capable of surviving even a single hit by a 21in torpedo.