The way the submarine sends a signal for help in distress

Immediately after the ship was in distress, the crew will broadcast emergency calls to the center, and at the same time launch signal buoys to inform the ship's position of distress. Depending on the severity of the problem, the battery may be disconnected and only the battery will be used, according to Howstuffworks.

Deep diving rescue ship (DSRV).(Photo: Howstuffworks).

Rescue efforts must take place urgently, usually within 48 hours of the incident, because the crew faces a lot of risk when the submarine falls into the ocean.The most dangerous is the risk of sea water entering the ship. Besides, they also face a lack of oxygen , high levels of carbon dioxide and a sharp drop in temperature as the on-board heating system stops working.

After receiving the rescue signal, a large ship carrying rescue facilities such as a deep-diving rescue ship (DSRV) , diving bell and steam buoy were quickly dispatched to the ship's distress. The DSRV will dive into submarine positions, cling to the upper side of the ship and connect to the "escape compartment" to create an escape route (the escape compartment is usually located on the upper side, the top of the submarine, is Special design in case of rescue).

The large ship contains rescue equipment such as deep-diving lifeboats, diving bell and steam buoys approaching the position of the submarine in distress.(Photo: Thinkdefence).

The enemy corpses trapped in the submarine will be evacuated to the DSRV through the emergency exit. In many cases, dive bells (deep diving equipment for divers) can be sent down to support rescue operations. When all crews are removed from the submarine, steam buoys will be mounted around the hull and then inflated to bring the submarine to the surface.

Rescue operations and salvage submarines also depend on many factors such as the depth of the ship in distress, weather conditions at sea, flow conditions and seabed topography.