According to developers Raytheon, the Phalanx CIWS is a "rapid-fire, computer-controlled, radar-guided gun that can defeat anti-ship missiles and other close-in threats" (Picture: US Department of Defense).
The Royal Navy welcomed the HMS Queen Elizabeth back to Portsmouth earlier this month, noticing a slight change in appearance.
Hidden under a white veil, the installation of the weapon system is already well underway.
This tweet came in from the ship following a successful visit to the US:
So, what does this technology do?
Designed to eliminate threats from anti-ship missiles and enemy aircraft that have pierced other lines of defence, the Phalanx Close-In Weapons System features include a 20mm M-61A1 Gatling cannon, search and track radar, infrared camera and control stations for visual tracking in the Block 1B model.
The rapid-fire technology has been installed on all US Navy surface combatant ships, alongside vessels belonging to over 20 allied nations.
HMS Queen Elizabeth is being armed with three Phalanx systems, each one capable of emptying a 1,550-round magazine at 4,500 rounds-per-minute.
As the cannons are to be called upon as a last resort, the effective range is approximately 9 kilometers.
Compared to a range of air-to-surface missiles, this is relatively short.
However, with each round released at 1,100 meters-per-second, the crew on board will feel much safer when the installation is complete.