Submarines

The method by which a modern submarine controls its depth is dynamic. It involves the use of the planes on the submarine, and the trim tanks inside the pressure hull. Let's take a look and see what's up.

Submarines have ballast tanks outside the pressure hull. These tanks have valves in the top called vents, and they have openings in the bottom. When the vents are closed and the tanks are filled with air, the submarine has positive buoyancy and it floats. When the vents are open, water pressure from below (through the openings in the ballast tanks) forces the air out of the top, and the tanks fill with water. With the buoyancy of the air in the ballast tanks gone, the submarine sinks. This is fairly simple and obvious. But there is more to the story.

Inside the submarine are other tanks called trim tanks. A logical setup is to have a set of them up forward and a set back aft. These tanks can be filled with seawater or can be pumped dry, and this is normally done with the submarine's trim pump, which is usually controlled from the ballast control panel. You can see what's coming now if we tell you one more thing. The boat has sets of planes that act as hydrofoils when the craft is moving through the water.

Picture a submarine with a set of planes in the stern (along with the rudder) and a set of planes on the sail. The sail is the superstructure somewhere in the "middle" of the submarine, and it houses the parts of the periscopes that are outside the pressure hull. With the submarine under way and submerged, water is moving over the planes, and the planes can act to push the boat up and down. It's like flying through the water with little "wings" out there to maneuver with. Obviously, the stern planes can effect a dramatic change in the way we "point" the submarine. Tip the stern planes up, and water pressure drives the stern of the boat down and points the bow up. Tip the stern planes down, and the opposite happens. Let's ignore the stern planes for now as we usually keep them at zero degrees unless we need to change depth rapidly. So what about the planes on the sail?

The sail planes are sometimes called the fairwater planes. They are located near the longitudinal center of gravity/buoyancy of the boat. That translates into their being able to act to push the whole boat down in the water when they are tipped down, or their being able to push the whole boat up in the water when they are tipped up. This assumes the boat is trimmed properly and is neutrally buoyant. It is the trim tanks that trim the boat so it is not bow heavy or stern heavy, and we can pump to both the forward and aft trim tanks to achieve neutral buoyancy.

Control of depth of a submarine that is under way, at least one with fairwater planes along with the stern planes, is done through a combination of the pumping of water into or out of the trim tanks and the use of the fairwater planes. The situation differs very little when we consider a boat with bow planes and stern planes. The ballast control panel operator will be working the hardest to keep the boat trim and make holding depth easy for the planesman.
Hovering is a precise maneuver, and is typically used by boats in preparation for surfacing through the ice, or for vertical missile launch ops where a stationary platform is required.

Hovering requires precise trim ballast tank control. Trim tanks are used to maintain Neutral Buoyancy while submerged, as well as to compensate for buoyancy and variable ballast changes when moving through depths or different temperature zones in the ocean. Once the boat is at an all-stop bell, the Ballast Control Panel (BCP) operator (the Chief of the Watch) will bring in or pump out the required amount of water from the trim tanks to hover. This can be tricky when you're trying to surface under the ice through a polynya (thin ice pond) as currents can move you when you move from a hovering/stationary position at depth to a slow ascent. It's not uncommon to get pushed into thick ice while making the transition.

For vertical launch missile ops, the boat must re-hover after a launch to regain a stable platform.

Torpedoes are shot from submarines, not "fired". "Fire" is a Hollywood term when referring to a torpedo launch; in real life, the word "fire" means only one thing on a submarine, so that there is a clear distinction between the two terms.

Torpedoes are shot from submarines using one of two methods: water impulse ejection, or swim out. Both methods have been used for decades, since the beginning of modern submarine designs.

Swim outs are rarely, if ever, used in modern submarines, unless there's an emergency or the impulse system is down. If it's necessary, the torpedo tube is flooded, and the outer tube doors are opened, the torpedo engine is activated, and the weapon "swims out" of the tube toward the target.

Before 1969, torpedo electrical checks were performed with the weapon on the rack in the torpedo room. Since the loss of the USS Scorpion, widely believed to have been sunk by a hot-running torpedo during electrical checks that detonated before deactivation, all torpedoes are now electrically checked while the weapon is in the torpedo tube. This is a precaution in case the weapon engines activate during checks; if it does, it can swim out or be ejected.

Water impulse ejection is the most common method. Each horizontal torpedo tube, when flooded, is connected via another vertical tube to a third tube which has a piston ram in it. One side of the piston has water, which is the same as the water which floods the tube. The other side is connected to a high pressure air flask, capable of dumping about 3000psi instantly into the air side of the piston ram.

During target tracking, when a target shooting solution is calculated (both by hand, plot, and computer) the information is fed electronically into the torpedo's guidance system. The Commanding Officer will order "Firing Point Procedures" in the Control Room, which is the final step before launching the weapon. At the proper angle, and when the weapon is ready, the CO will order "Shoot", and the crew will send a command to the air flask, which immediately dumps air into the piston ram. The air pressure, which is higher than the outer sea pressure, forces the water out of the tube, along with the the torpedo itself. Once the torpedo has traveled a certain distance from the boat, the engine will start, and it will begin its journey toward the target. As a safety precaution, the torpedo needs to be a certain range away from the boat before the warhead arms to prevent it locking onto the boat it was launched from. If you're sleeping next to the tube in one of the crew spaces, or in the torpedo room itself (portable racks), the noise will wake you up if you're not used to it.

Though most torpedo solutions are derived over time by tracking a target, there are procedures to deal with an immediate threat as well. If Sonar detects a hostile torpedo in the water being launched, the hostile torpedo bearing can quickly be input into the torpedo guidance system, and "Snap Shot" toward the hostile torpedo's bearing. All modern torpedoes are both wire-guided and have active-passive homing sonar. If they lock onto a target, they are nearly impossible to evade, despite what Hollywood would have people believe.

Ejecting water in an empty tube during tube testing is called shooting "water slugs". It's not powerful enough to affect a boat underway, but its' strong enough to move a mooring bumper in port while moored next to a pier.

A submarine is said to sail, either on the surface or submerged.

A submarine is driven, but similar to the way a plane is flown. It takes a team of men to drive the sub. You have a helmsman, planesman, and Chief of the watch controlling depth, direction, and angle of the boat. In the engineering department, you have the reactor plant operator controlling steam production, and a propulsion operator that controls the amount of steam going into the steam turbines that control speed. There are more people involved in less direct jobs than this but this will give you a rundown.

To give you an idea of what it's like: imagine 5 guys that are only 6 inches tall trying to drive a car. You have one on the gas, one on the brake, two on the steering wheel, and another yelling out at everyone to go, stop, or turn.

submarine

Submarines use them.