Submarines float to the surface thanks to air-filled ballast tanks, which are fitted with valves at their tops that open when it's time for the submarine to dive. But, how deep can a military submarine dive?

Today we present to you the 10 deepest operational submarines in the world.

10. TRIUMPHANT CLASS SUBMARINE

The French Navy's TRIUMPHANT-class ballistic missile submarine, also known as the next generation nuclear ballistic missile submarine, forms the oceanic part of the French nuclear deterrent strike force.

The propulsion system of the submarine is a nuclear turbo-electric system based on a type 15 pressurized water reactor which produces a power of 150 megawatts.

The underwater displacement of the submarine is 14,335 tons, and its test depth is more than 400 meters.

9. BOREI CLASS SUBMARINE

The BOREI CLASS is a self-built nuclear ballistic missile submarine of the Russian Navy. It is a fourth-generation nuclear ballistic missile submarine with a lower sonar detection rate than its predecessor.

Another advancement is a jet-pump propulsion system, which also works thanks to an ok 650 nuclear reactor and an AEU steam turbine. It is the first aircraft in Russia to use a pump jet propulsion system.

8. YASEN CLASS SUBMARINE

The ASEAN-class, also known as the YASEN-CLASS, is a nuclear-powered submarine equipped with cruise missiles, designed by Malakit and built for the Russian Navy by Self mash.

Based on the Akula and Alpha class designs, the ASEAN class is expected to replace the Russian Navy's current Soviet-era nuclear attack submarines.

It is powered by two 650 kpm pressurized water reactor turbines, or 43,000 shaft horsepower.

7. AKULA CLASS SUBMARINE

AKULA CLASS Has a measuring flight of 450 meters The Akula class is a nuclear-powered attack submarine that was first deployed by the Soviet Navy in 1986.

It is one of seven diving submarines in service in the world. A 190 megawatt vm5 pressurized water reactor and a gt38 turbine constitute the main machinery, with two types of 750 horsepower diesel auxiliaries providing emergency control.

A seven-bladed fixed-pitch propeller, with a test depth of 480 meters, is driven by the submarine's propulsion system.

6. SEAWOLF CLASS SUBMARINE

The SEAWOLF class is a class of nuclear-powered fast attack submarines currently in service with the United States Navy.

A GE pwr s6w Best reactor system powers the nuclear-powered sea wolf.

Using two 52,000 horsepower engines, a pump jet thruster, a single shaft and a secondary propulsion submerged engine, the Seawolf-class submarines are capable of a test flight of 490 meters.

5. TYPE 209 SUBMARINE

TYPE 209 – A German diesel-electric attack submarine that was exported to 13 countries, with 61 submarines built and commissioned between 1971 and 2008.

The test depth of this submarine is the same as the previous one, 490 meters, and its propulsion is of the diesel-electric or diesel type with a single shaft and a power of 6,100 horsepower on the shaft.

4. VANGUARD CLASS SUBMARINES

The VANGUARD class is a Royal Navy nuclear-powered ballistic missile submarine. The pwr2, a new pressurized water reactor from Rolls-Royce, was created specifically for the Vanguard class.

The reactor drives two GEC steam turbines connected to a single-shaft pump-jet thruster, which gives the submarine a maximum submerged speed of over 25 knots.

They are the largest submarines ever built in the UK, with a displacement of 15,900 tonnes when submerged.

3. SIERRA-CLASS SUBMARINES

SIERRA CLASS - Nuclear-powered attack submarine that was designed for the Soviet Navy and is now in service with Russia.

The class is distinguished by its light and heavy titanium pressurized hull, which allows submarines to dive to greater depths, minimize radiated noise and improve torpedo resistance.

The Sierra class has a test flight of around 520 meters and operates with a single ok 650 pressurized water reactor.

2. 039A CLASS SUBMARINES

The 039A-CLASS, also known as the Yuan-class, is a class of diesel-electric submarines built for the Chinese People's Liberation Army Navy.

According to an initial assessment by the US Naval Institute, it is China's first air-independently powered submarine and is expected to be one of the quietest classes of diesel-electric submarines in service.

The Yuan class was created primarily as an anti-ship cruise missile platform capable of remaining submerged for long periods in hard-to-reach shallow littoral areas. It goes down to a depth of 550 meters.

1. OSCAR-CLASS SUBMARINES

The OSCAR CLASS is the deepest submarine in service in the world to date. It is a nuclear-powered cruise missile submarine that was originally designed for the Soviet Navy but is now in service with Russia.

The Oscar class test depth is 830 meters. Some of these ships are expected to be modernized under the 949 am project to extend their service life and improve their combat capabilities.