The location of L'Ile Longue (Long Island) naval submarine base.
A long side view of the L'Ile Longue naval installations.
L'Ile Longue includes three zones: yellow zone, red zone and blue zone.
L'Ile Longue is home to Triomphant class submarines of Strategic Oceanic Force (FOST).

L’Ile Longue (Long Island) submarine base is located south of the harbour of Brest. The base is the homeport of the ballistic missile nuclear-powered submarine (SSBN) of the French Navy (Marine Nationale). Four Triomphant class submarines based at L’Ile Longue form the Force Océanique Stratégique (FOST), France’s nuclear arsenal.

The base is occupied by 2,400 personnel including civilian and military forces.  L’Ile Longue is one of the most secret and well protected bases in France.

Location and layout

L’Ile Longue is a small piece of land in the harbour of Brest connected to the peninsula by a causeway. The peninsula is a stone plateau bordered by cliffs.

The isthmus was initially a mere sand bank and was improved with a stone pathway laid in the 19th century. It was widened and changed into a parking area during the construction of the base.

The base includes two dry docks, numerous habitation, engineering and defence buildings.


“L’Ile Longue is a small piece of land in the harbour of Brest.”

L’Ile Longue served as a quarantine station during the early French occupation. It was used as an internment camp for German citizens captured in September 1914 from the ship Nieuw Amsterdam by the French 2nd Light Squadron. The camp was closed when the last prisoners were released in December 1919.

L’Ile Longue played a vital role in the defence of the Brest until the German occupation.

Germany used L’Ile Longue as an anti-aircraft battery during WWII. Megalithic monuments were destroyed and bunkers were constructed. This installation remained active until 1944.

In 1965, President Charles de Gaulle selected L’Ile Longue as home base for the nuclear ballistic missile submarines of the French Navy. Work began in 1967 and took five years to complete. The peninsula was revamped and 30ha of land was added. L’Ile Longue hosted the first submarine, the Formidable, in September 1970 prior to its completion. The base became operational in 1972 and the submarine Le Redoutable left L’Ile Longue for her first patrol.

L’Ile Longue base operations

L’Ile Longue submarine base provides support, logistical supply and reconditioning material for nuclear ballistic missile submarines. The base undertakes loading and unloading of strategic missiles as well as loading and unloading of fuel components for nuclear steam supply.

The port-based French nuclear submarine ballistic missiles undergo maintenance at the base. Each submarine undergoes a maintenance period of forty days at L’Ile Longue after returning from patrol.

The submarines also visit L’Ile Longue for the removal of missiles and nuclear fuel before undergoing major overhaul at Brest. All these functions are executed under stringent guidelines relating to nuclear safety, environmental protection and protection of the secrecy of national defence.

The Triomphant class of ballistic missile submarines based at L’Ile Longue are: Triomphant (S616), Téméraire (S617), Vigilant (S618) and Terrible (S619).

Garrison facilities

The base carries out maintenance on submarines between patrols. It is composed of colour coded zones.

The yellow zone includes the harbour and installations to accommodate the submarines. The reactor workshop is located between two basins. The submarines can be docked in two roofed 200m-long docks. All maintenance on the nuclear reactors are carried out in this workshop.

“L’Ile Longue is one of the most secret and well protected bases in France.”

The parts of the nuclear reactor are separated and inspected, and the fuel can be stored in a 170m-long pool. The principal movable workshop for intervention (Amip) is also available for maintenance of submarines.

The red zone consists of bunkers for the assembly, storage and maintenance of missiles and nuclear warheads.

The assembly of warheads is carried out in the buildings of the CEA annex of the L’Ile Longue pyrotechnical section.

The blue zone houses security installations and personnel, recreational facilities and barracks.

Chemical pyrotechnics for the missiles and conventional warheads are stored in Guenvénez.

Other base facilities

The base has living quarters in the blue zone area for active duty members and their families.

Other facilities include a commissary, a child care centre, restaurants and recreational areas.