Royal Navy’s HMS Agamemnon, the sixth Astute-class submarine, is another step closer to joining the UK’s in-service submarine fleet, following the completion of its first dive.
After being commissioned last month, the dive took place over two days and saw the boat submerged in water in the safety of a dock at BAE Systems in Barrow-in-Furness, under the control of the Royal Navy crew. King Charles III commissioned the Royal Navy’s newest nuclear-powered attack submarine on September 22, 2025.
A trim dive is a key phase of a submarine’s testing and commissioning prior to her sailing for the first time and joining the in-service fleet. This consists of two activities, a basin dive and a trim and inclining experiment.
The basin dive is where many on-board systems are tested, including the ballast tanks, which ensure the boat can surface. The trim and inclining experiment is to confirm the center of gravity of the submarine and is measured by naval architects in both surfaced and submerged conditions.
According to the officials, to measure the center of gravity of the submarine, 16 tonnes of lead weights are brought on board and moved side-to-side. This movement is also measured by hand using pendulums hung between decks, a method that has been used by naval architects since the 1700s.
The results from this also calculate the precise weight and stability, showing how she will perform in-service.
The trials were conducted by BAE Systems and the ship’s staff, and activity was monitored by SDA and Ministry of Defense naval architects and overseers.
HMS Agamemnon was officially named in April 2024 and launched in October 2024. The boat is 97 meters in length and has a displacement of 7,400 tonnes. The Astute-class submarines are the UK’s current attack submarines.
The vessel will join HMS Astute, HMS Ambush, HMS Artful, HMS Audacious and HMS Anson in service.