The answer to why submarines are black might seem straightforward, but it's not quite as obvious as it seems and is closely tied to why car tyres are the same colour.
Let's delve into a bit of the history of submarines before expanding on that.
It was during the First World War that submarine hulls started to be painted grey and the decks black to provide camouflage.
However, once the enemy's aircraft started flying over water, submarines could be spotted when they weren't fully submerged.
Before nuclear power, diesel-powered submarines contained leading-edge technology but, compared to today's modern subs, were slow underwater vessels and spent a lot of their time on the surface to refuel and resupply.
Fast forward to 1955, when the US Navy created the first nuclear-powered submarine, USS Nautilus, an underwater vessel that changed the course of maritime history.
Due to the now vastly increased time a submarine could spend submerged underwater, and wanting to make the vessels as difficult to find as possible, led to a rethink when it came to the colour scheme.
Warships are grey to reduce the chance of the vessels being spotted by the enemy.
For example, when a vessel is close to the horizon, a haze grey exterior can make it hard to identify accurately, even more so in foggy or cloudy weather conditions.
Keeping that in mind, why are submarines black when they are also found at sea?
You might have seen posts on social media about which swimming costume colour parents should choose to help keep their children safe in the water in case they should find themselves unable to swim and go underwater.
Neon yellows and greens are more visible the further the costume sinks underwater whereas the blue, white and black swimwear becomes barely visible very quickly.
The same applies to submarines.
Of all the colours of paint, black is the most durable and reflects the least amount of light, helping to camouflage the vast vessel when it is near the surface.
And according to reports, there is barely any light once you reach 200 metres into the ocean.
The test depth of a submarine is the maximum depth an underwater vessel can operate under normal peacetime circumstances.
Submarine test depth information is often classified to prevent enemy forces having a tactical advantage.
Official statistics released by the Royal Navy about its stealthy and powerful submarine fleet include the vessels' lengths, top speeds and weight – not the test depth.
However, a testimony of a submariner on the Royal Navy's official website reveals a depth where there is rarely any light.
Chef (Submariner) CH Hayes, said: "You can't beat the buzz of working in a kitchen – especially when you're 200 metres underwater."
But submarines aren't black for that reason alone.
Sometimes the perfect material for the job just happens to be black.
It's all about anechoic tiles.
According to the Royal Navy, Astute is covered by "more than 39,000 anechoic tiles that absorb active sonar and reduce noise radiated from within the boat."
Photos of Royal Navy submarines resurfacing show off these impressive tiles for the world to see.
Reports say anechoic tiles make detecting submarines more difficult because their unique design distorts sonar waves being used to discover the vessel's location.
In layman's terms, anechoic tiles to submarines are like the invisibility cloak to Harry Potter.
The durable, porous material absorbs active sonar waves helping to make them less visible underwater.
But what are active sonar waves?
Just like whales and dolphins, submarines rely on sonar (sound navigation and ranging) to navigate in water.
To find an enemy submarine, the Royal Navy uses two types of sonar – active and passive.
Active sonar is a pulse of sound – a 'ping', let's say – that travels through water to an unknown object, only to return, be analysed and interpreted to give sonar operators an idea of what is around them.
However, when a sound wave hits an anechoic tile, it is partially absorbed so, when it reflects back, it is reduced and distorted – confusing the enemy as to the submarine's whereabouts.
There is, however, a downside to using active sonar.
There is a risk the 'ping' sound could be detected by enemy submarines so, more often than not, passive sonar is used to protect the vessel's location.
Passive sonar is where operators listen for sound in order to detect a ship or other submarine and determine the trajectory.
And thanks to black anechoic tiles reducing the sound coming from within submarines, doing that isn't as straightforward as you might think.
So why are submarines black?
Because their invisibility cloak, anechoic tiles, just happen to be black.
And why are they black?
Rubber anechoic tiles contain carbon black, an odourless, insoluble, ultralight, fine black powder, to make them more durable underwater.
The same goes for car tyres. Remember the connection between submarines and car tyres?
Rubber is naturally white, not a colour usually associated with car tyres which are made up of a variety of different types of the highly versatile and malleable material.
To increase the durability of tyres, a substance known as carbon black is added to reduce wear and tear over time, increase tensile strength and protect the rubber from UV light damage.
The same can be said for anechoic tiles.
Also made of rubber, anechoic tiles used on submarines contain carbon black to increase their durability when submerging and resurfacing over and over again.
So that is why submarines are black.