The Control Room contains practically all the controls necessary to dive, navigate and fight the submarine
The helmsmen’s "wheel”, a tapper-bar in HMS Alliance, is forward with the gyro and magnetic compass repeaters, main motor and engine-room telegraphs, internal inter communication systems and a voice pipe to the bridge which had to be shut off when diving.
Depth was changed and maintained by the two hydroplane operators. Broadly speaking, the fore-planes controlled the depth and the after-planes regulated the bow angle up or down; but a skilled after-planesman (the Coxswain at diving stations) knew exactly the amount of angle required and could virtually change and keep depth by himself; in any event the two planesmen worked very closely together. The planes became more effective as speed was increased but with a good trim it was possible to maintain depth accurately at speeds down to about 1½ knots. If the submarine had achieved the ideal state of neutral buoyancy, displacing exactly her weight submerged in water, it was sometimes possible to hover stopped, especially if there was a layer of denser water to sit on at a convenient depth.
Depth changes using the forward and after planes
To change depth the boat was simply angled up or down by the hydroplanes and the propellers drove her to the ordered depth. Far from adding water to go deep, it was necessary to pump out about 75 gallons for every 100 feet to compensate for the hull compressing and hence displacing less. The normal maximum diving depth for Alliance was 500 feet but a safety factor allowed her to go much deeper than this without risk of the hull collapsing. Compressibility was quite noticeable when going deep: the radar office wooden door, for instance, had a habit of bending as the enormous pressure of water squeezed the submarine.
A submarine diving and surfacing using the main ballast tanks
Diving and surfacing were simple procedures. On the surface, Alliance like all submarines, rode on the air in the main ballast tanks, which ran along the hull on the outside. Large free-flood holes in the bottom were always open; as soon as the main vents were opened hydraulically from the diving panel at the after end of the Control Room the supporting air was released. This allowed water to flood the tanks and destroy the 235 tons of positive buoyancy that had kept the boat on the surface. A special internal tank, Q tank, could be flooded separately to give temporary negative buoyancy for quicker diving or for changing depth rapidly; it was blown by high pressure air just before the ordered depth was reached. The main vents were shut when fully submerged so that the boat could be brought to the surface at any time by blowing water out of the main ballast tanks by means of high pressure air stored in air bottle groups. The main ballast blowing valves are close to the main vent hand-levers on the diving panel. It took a considerable time to re-charge the HP air bottles; so the HP blows were only used to achieve just enough buoyancy to break surface. The remaining water in the main ballast tanks was then forced out with a rotary, eccentric low-pressure air pump known as the Blower.
Blowing Panel (right) and Trim Pump (Left)
The trim changed continually at sea as stores, fresh water and oil fuel were used up and when the density of the surrounding seawater altered from area to area and at different depths. The fore-and-aft angle was corrected by pumping water from forward to aft and vice versa along a trim line. Bodily weight was adjusted by a main line system connected to all internal tanks which allowed seawater to be pumped out from selected tanks or flooded in by sea pressure as required. The state of the trim was largely judged when dived by noting what action the planesmen had to take to keep the boat level at the ordered depth. For example, a bow-up angle, with the planes at hard-a-rise, which did not result in the boat coming up obviously meant that the boat was heavy and the Officer of the Watch pumped out water accordingly. Just how much to pump or flood was learned by experience and was an important part of an officers training.If a steep bow-down angle resulted from any cause - flooding forward for example - the quickest way to right the situation was to order a number of hands to pass from forward to aft at the rush; an average sailor weighed the equivalent of 15 gallons and could move much more quickly than water through the trim pump!There are two periscopes in the Control Room. The search periscope was used, as its name implies, for finding targets and safe navigation. It has a “round-about” seat which the operator could revolve electrically with foot pedals to save him having to turn the heavy instrument by hand — an important consideration when keeping a continuous periscope watch while snorting. Shades and focusing attachments are fixed to the eyepieces. The operator could search in a vertical plane by using one twist grip and was able to change the magnification from 6 x to 1½ x with the other grip; the 1½ Low Power magnification gave the impression of normal vision. The attack periscope, which is now seen in the lowered position, has a much smaller head and slightly poorer monocular vision; it was used during the closing stages of an attack to reduce the risk of detection and was only exposed for a few seconds at a time. Both periscopes incorporate a range finding device.
The navigational plot and automatic plotting table are on the starboard side of the Control Room with various navigational instruments close at hand including the automatic Decca Navigator, a radio-fixing device which, so long as an aerial was sufficiently exposed, gave the submarine’s position continuously and accurately.
The Royal Navy Submarine Museum . Haslar Jetty Road . Gosport . Hampshire . PO12 2AS
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