AIP

Air-independent propulsion (AIP), or air-independent power, is any marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen (by surfacing or using a snorkel). AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels.

surface propulsion

Opencycle systems

Closed cycle diesel engine

Closed cycle steam engine

Fuel cell

This technology uses a submarine diesel engine which can be operated conventionally on the surface, but which can also be provided with oxidant, usually stored as liquid oxygen, when submerged. Since the metal of an engine would burn in pure oxygen, the oxygen is usually diluted with recycled exhaust gas. Argon replaces exhaust gas when the engine is started.

Siemens has developed a 30–50 kilowatt fuel cell unit, a device that converts the chemical energy from a fuel and oxidiser into electricity. Fuel cells differ from batteries in that they require a continuous source of fuel (such as hydrogen) and oxygen, which are carried in the vessel in pressurized tanks, to sustain the chemical reaction.

1. On the Surface (Diesel Engine Mode)

• The submarine uses a diesel engine when it is on the surface or snorkeling (just below with a snorkel mast).

• The diesel engine does two things:

  1. Powers the electric generator to run the submarine.

  2. Recharges the batteries for underwater use.

• Since diesel engines need air, this mode only works when the submarine is surfaced or snorkeling.

2. Underwater (Fuel Cell AIP Mode)

• When submerged, the fuel cells take over and provide quiet, long-lasting power.

• The fuel cells combine stored hydrogen and oxygen in an electrochemical reaction to produce electricity—no combustion, no moving parts, and very little noise.

• This electricity powers the electric motor, which turns the propeller.

• Why is this important?

  • Unlike traditional diesel-electric submarines, which rely only on batteries, the fuel cells allow the Type 212 to stay underwater for weeks without surfacing.

  • This makes the submarine much stealthier and harder to detect.

3. High-Speed Underwater Travel (Battery Mode)

• When the submarine needs to move fast (e.g., during an attack or escape), it switches to batteries.

• The batteries provide a quick burst of power for the electric motor, allowing high-speed movement.

• However, batteries drain quickly, so the submarine only uses this mode when necessary.

Components

- Navigation system

- Communication system (int./ext.) incl. radio room

- Sensors (underwater)

- Sensors (surface)

- Antennas, hoistable masts

- Weapon control systems

- Networks/LAN incl. ext. integrated systems

- Entertainment systems

- Ammunition (torpedoes, missiles, mines), weapon systems

- Defence systems incl. effectors

- Data recording and evaluation (incl. proprietary development)

- Shipboard simulators

- Training facilitie