To evacuate a submarine, the method largely depends on whether the vessel is on the surface or submerged, with sophisticated systems in place for underwater emergencies.
Submarine Evacuation: A Multi-faceted Approach
Evacuating a submarine, especially when submerged, is a complex operation requiring specialized equipment, rigorous training, and adherence to strict protocols. While surface evacuation can be akin to abandoning any vessel, deep-sea escape involves advanced life-support and pressure-equalization technologies.
Evacuation on the Surface
If a submarine is on the surface and needs to be evacuated, the process is relatively straightforward. Crew members can exit through the various hatches located on the sail and hull. In such scenarios, personnel would typically transfer to nearby rescue vessels, life rafts, or even swim to safety if close to shore, much like abandoning a surface ship.
Evacuation While Submerged: The Deep Escape
Evacuating a submerged submarine is significantly more challenging due to the immense pressures, cold temperatures, and the need to transport personnel safely from a high-pressure environment to the surface.
Escape Trunks: The Primary Method
For individual or small-group escape from a distressed submarine, specialized air locks known as escape trunks are the primary method. Modern submarine deep escape systems, effective down to a maximum depth of 600 feet, utilize these trunks. On current U.S. Navy submarines, these trunks are designed to release two survivors per cycle. After donning specialized buoyant ascent escape suits (sometimes referred to as "Steinke hoods"), survivors enter the trunk, and the lower hatch is then securely closed. The trunk is then flooded with seawater and pressurized to match the external sea pressure. Once pressure equalization is achieved, the upper hatch opens, allowing the survivors to ascend rapidly but safely to the surface.
Key Steps in Escape Trunk Evacuation:
- Preparation: Crew members don individual escape suits, which provide buoyancy, thermal protection, and a breathable air supply for the ascent.
- Entry: One or two survivors enter the escape trunk, and the lower internal hatch is sealed.
- Flooding and Pressurization: The trunk is rapidly flooded with seawater and pressurized to match the external ocean pressure.
- Upper Hatch Release: Once internal and external pressures are equal, the upper hatch opens, releasing the survivors into the sea.
- Controlled Ascent: The escape suit's buoyancy propels the individual to the surface, with a controlled ascent rate managed by the suit's design and the survivor's training.
Rescue Submersibles and Diving Bells
For situations where the entire crew needs to be rescued, or if crew members are injured and cannot use individual escape trunks, external rescue assets are deployed. These include:
- Deep Submergence Rescue Vehicles (DSRVs): These are small, highly maneuverable submersibles designed to mate with a distressed submarine's escape hatches. They can transfer multiple personnel at a time from the disabled submarine to a mother ship on the surface. Examples include the U.S. Navy's DSRV Mystic and Avalon (now retired, replaced by SRDRS).
- Submarine Rescue Diving and Recompression System (SRDRS): This is a modular, air-transportable system used by the U.S. Navy, which includes a Pressurized Rescue Module (PRM) that functions similarly to a DSRV, capable of rescuing up to 16 people at a time.
- Diving Bells/Transfer Under Pressure (TUP) Systems: These are often used in conjunction with saturation diving facilities for more complex rescue and medical operations, allowing for transfer under pressure to avoid decompression sickness. The NATO Submarine Rescue System (NSRS) is an example of an international system employing such capabilities.
Free Ascent (Last Resort)
In extreme, last-resort scenarios, a "free ascent" might be attempted without specialized escape suits or trunks. This is an incredibly high-risk procedure, requiring specific training for a controlled exhalation during ascent to prevent lung overexpansion due to decreasing pressure. It is generally only considered when no other options are available.
Key Considerations for Submarine Escape
- Depth Limitations: Direct individual escape systems, like those using escape trunks, are designed for specific depth ranges. As mentioned, modern systems are effective down to a maximum depth of 600 feet. Beyond this, rescue submersibles become the primary, or only, viable option.
- Training and Equipment: Submarine crews undergo rigorous training for escape procedures, including practicing with escape suits and understanding the physics of pressure changes.
- Environmental Factors: Water temperature, currents, and the presence of hazards around the submarine all impact the feasibility and success rate of an escape or rescue.
- Medical Considerations: Rapid ascent carries risks of decompression sickness and other barotrauma, which are mitigated by suit design, training, and the availability of recompression facilities on rescue vessels.
Step-by-Step Escape Trunk Procedure
The following table illustrates the general sequence for escaping a submerged submarine via an escape trunk:
| Stage | Description |
|---|---|
| 1. Donning Suits | Survivors don specialized buoyant ascent escape suits (e.g., Steinke hoods or similar). |
| 2. Enter Trunk | One or two survivors enter the escape trunk. The lower internal hatch is then securely sealed. |
| 3. Flood & Pressurize | The trunk is rapidly flooded with seawater and its internal pressure is equalized with the external sea pressure. |
| 4. Upper Hatch Open | Once pressure is balanced, the upper external hatch of the trunk opens automatically or manually. |
| 5. Ascent | Survivors ascend to the surface, buoyed by their escape suits, maintaining a controlled rate of rise. |
| 6. Surface Recovery | Survivors are located and recovered by surface vessels or rescue teams. |
Importance of Safety and Readiness
The ability to evacuate a submarine successfully hinges on robust engineering, comprehensive safety protocols, and continuous, realistic training for the crew. These measures ensure that in the event of an emergency, every possible step is taken to preserve life.
