The British nuclear submarine HMS Vanguard has returned to its home port after a record 204-day patrol, the longest in its class.

According to Navy Lookout, the submarine left Faslane in late August and remained submerged for more than six months.

A few weeks before its return, another nuclear-armed submarine departed on patrol.

In recent years, the length of British submarine patrols under the nuclear deterrence program has increased significantly.

The last eight missions have each exceeded five months.

HMS Vanguard’s latest deployment, lasting nearly 6.7 months, was among the longest.

Extending patrol durations allows for more time between deployments for maintenance, crew recovery, and training.

However, prolonged underwater missions pose technical and psychological challenges.

Extended stress increases the risk of mechanical failures, while the confined environment can impact crew well-being.

The submarine likely surfaced several times to replenish supplies, as its refrigeration storage is designed for three to four months of autonomy.

Last year, British media reported that crews on extended patrols had to switch to limited rations near the end of their missions.

On March 21, the Royal Navy announced that the keel of the first Dreadnought-class submarine, HMS Dreadnought, had been laid at BAE Systems’ shipyard in Barrow-in-Furness.

The new submarine will be the first of four Dreadnought-class vessels set to replace the aging Vanguard-class fleet.