In the early 20th century, the French equipped their surface fleet with one of the most unique and formidable weapons in naval history : this is the fascinating story of the 340mm/45 Modèle 1912 gun, which saw service in two wars, both on land and at sea, whether in turrets, emplaced, cradled, or on rails. And in a dramatic turn of events, some of the 340s France built even saw action against each other during the final stages of WW2.

The rugged coastal region of Bretagne is surely one the most striking landscapes in Europe. Rocky cliffs alternate with mystical coves and inlets seemingly without end, while its longer stretches of windswept coast are dotted with dunes, and covered in lush seaweed. This used to be the mythical Armorique: A craggy and untamed land whose most recognised geographical feature is the Gulf of Morbihan. It is an immense natural harbour, so much that its given name in Breton translates to “The Little Sea”. Legend had it that it contained as many islands as there were days in a year, and the fertile region it adorns has been home to a hardy and fiercely independent people since ancient times. They were merchants, seamen, pirates, warriors and noblemen, and built megalithic Dolmen, giant Menhir monoliths, and stone circles in monumental religious centres like Carnac. Their ancient culture and explosive temperament has been immortalised in the comic book series The adventures of Asterix the Gaul.

The Gulf of Morbihan as seen from one of its many islands, Île-d’Arz

And then came la guerre. Shortly after the Fall of France in June 1940, the Nazis begin to build a number of fortified U-boot bases along the western Atlantic coast. The largest two of those bases, comprising 44 submarine pens to shelter 4 flotillas, were built between 1940 and 1942 in Lorient, and St.Nazaire. And between these, at the neck of the Quiberon peninsula, close to the small Breton village of Plouharnel, ample space was cleared to create a formidable battery. It was considered to be one of the most powerful artillery sites in the Atlantic Wall, and its unique guns have a fascinating story.

The Keroman Submarine Base at Lorient today

With a firing range of 38km, these 340mm coastal guns would be capable to interdict a huge area off the coast of Bretagne, denying naval access to the Gulf of Morbihan, and more importantly, protecting the Keroman Submarine Base at Lorient. Their arc of fire could also link up with that of the 240mm guns battery at Batz some 60km down the coast, which in turn protected the nearby St. Nazaire Submarine Base from seaborne intruders. For comparison, the coastal guns at Plouharnel boasted a longer range than the Bismarck, or any ship of the Royal Navy at the time. In fact, they had about the same range as those of a US Iowa class battleship, and only slightly inferior range than those of the Japanese Yamato class battleship : and these were perhaps among the heavier naval guns that ever saw action !!

A painting of the French Bretagne-Class Super-Dreadnought MF Lorraine, with her 340cm guns in 8x twin turret configuration

Origin of the guns

This naval comparison is not entirely coincidental. The coastal guns at Plouharnel actually emerged in the service of the French Navy circa 1912. The early 20th century was a monumental period for naval warfare, a time when the construction of ever heavier battleships by the powerful navies of the era resulted in a new class of warship, the so called Super-Dreadnoughts. It all began with HMS Dreadnought, a heavy British battleship launched in 1906. The enormous firepower she carried instantly tipped the balance of power at sea, and prompted a naval race without precedent among nations of the time. The French response to this event was the Bretagne class of battleships, a series of three Super-Dreadnoughts equipped with the 340mm/45 Modèle 1912 naval gun in 4x or 5x twin turret configuration as main armament – the type of barrel that was eventually stationed at Plouharnel.

An artist’s impression of the never built MF Normandie

The evolution of that class was to be the MF Normandie, first in a new ship class designed to deliver terrifying firepower out of its 12 guns in 3x quadruple turret configuration as main armament, and with never-seen-before propulsion capabilities. However, the Normandie class was cancelled at the outbreak of the first World War, and the 12 naval guns already built for it were transferred to the French army as surplus.


A St. Chamond French Canon de 340 modèle 1912 à berceau circa 1918

Conversion to railroad guns

As WW1 progressed, the warring nations switched their production from naval vessels to the more pressing needs of the Western front. The high demand for super heavy artillery, combined with the sudden availability of surplus naval guns of various calibres saw many of these mounted on carriages, and converted to railroad guns for use on land operations. The French Army launched a conversion programme for Normandie‘s twelve cannons. Half of them were converted by Schneider to Canon de 340 modèle 1912 à glissement (sliding, literally), a railroad gun that transferred the natural recoil of the gun to the section of track behind it. These were in fact delivered too late to participate in the war. The other 6 guns were converted by St.Chamond (the actual manufacturer of Normandie‘s guns) to Canon de 340 modèle 1912 à berceau (cradle, literally), using a hydro-pneumatic cradle system to absorb the recoil. All of the “cradle” guns saw action between 1916 and 1918, with two of them assigned to the US Army and one reinforcing the Italian army. At the end of the war, the railroad guns were mothballed in reserve.

A captured Schneider Canon de 340 modèle 1912 à glissement

This is a video of a French railroad gun exiting the cannon foundry at Ruelle-Sur-Touvre before the war (probably in the late 30s). It shows a Canon 380 mm / 45 model 1935 (yes – this was an even bigger naval gun than the 340mm, but that’s another story) mounted on what appears to be a St. Chamond à berceau cradle. I am just gonna leave this here so you can experience the action of a railway mounted naval gun. This is as close as it gets to what the ones based at at Baterie Plouharnel would have looked :

The guns in German service

The outbreak of World War 2 saw the railroad guns entering French service for a second time, and placed along its eastern border with Germany. After the Fall of France, most of these railroad guns were captured and pressed into the service of the German army. A number of the six “cradle” guns (some sources suggest three) were given to the Italians for evaluation toward the defence of their key Mediterranean naval base at Taranto. However, the Italians are not known to have actually deployed the guns, for lack of suitable ammunition : the 340mm caliber was specific to the French navy, which may explain this scarcity. And so the last of the “cradle” railroad guns were assigned to the Plouharnel battery in the Atlantic coast.

The battery layout at Plouharnel

The battery layout at Plouharnel shows emplacements for 4 railroad guns, not 3. That suggests that maybe the Italians received less than 3 “cradle” guns after all, or it may suggest that not all railroad guns at Plouharnel were à berceau. Some other sources suggest that St. Chamond only ever converted 4 guns to à berceau in the end, and that all of them were based at Plouharnel. Whatever the truth is, the fact remains that the battery seems to have accommodated 4 railroad guns near the coast. The railway track branches out between the villages of Plouharnel and Quiberon, allowing the gun carriages to move into the site and rest inside the concrete emplacements. Behind these, a series of personnel and ammunition bunkers, as well as ancillary structures such as a water cistern and electricity generators. And topping it all, a formidable observation and fire control tower that is still standing today.

The Observation and Fire Control Tower, with the Command bunker below

Such an important site would be expected to comprise a network of land and air defences too. I saw a type FL242 air defence bunker that would have contained a light or medium gun. Such emplacements are known to have existed in numerous locations along the Atlantic Wall, in places as disparate as Fjell in Norway, the Hague in the Netherlands, or the island of Jersey in the English channel. They were equipped with a searchlight, ammo stores and space to accommodate a crew of 8 or 9. A 2cm Flak 30/38/Flakvierling would have been an AA gun commonly emplaced in a FL242.

The top of a FL242 emplacement. Most of the bunker is buried under the sand.

Nearby, artillery and anti-tank defences can be seen. It has been suggested that this might have been an emplacement for 7.5cm PaK 40 anti tank gun, by virtue of a sign on one of its ammo compartments.

Facing the sea

I am not certain about that usage, however. Since these strong points seemed to point towards the sea, this might have defeated their supposed utility as AT emplacements.

Nature takes over

And this is the machinery and generator bunker in the distance.

The generator and machinery bunker

Plouharnel is a sizeable site, covering 2 sq km. There was much more to be explored than what I could cram into my quick visit. Speaking of quick visits, Feldmarschall Erwin Rommel toured the defences of the Atlantic Wall as the General Inspector of the Atlantic Defences. He is known to have visited Plouharnel batery in April 1944.

Rommel at Plouharnel, April 1944

The 340mm guns in action

We know that the 340mm railroad guns at Plouharnel saw plenty of action during WW1, but were these ever fired in anger during the WW2? I cannot be certain. They did provide a strong deterrent against any encroachment from the sea though, and maybe this is why I could find no record of them in action. But there are other, well documented stories involving French 340cm guns at war, and I will relate these ones instead, especially since they form a somewhat riveting narrative! We have to travel back in 1912 for this, at a time when the French navy were building the Bretagne class Super-Dreadnoughts. Three ships were ever launched in this class, the MF Bretagne, MF Provence, and MF Lorraine. By virtue of these and other major vessels, at the outbreak of WW2 France boasted the second largest fleet of capital ships in Europe (after the Royal Navy). But there was a 4th ship in the Bretagne class, ordered by the Royal Hellenic Navy. She was laid down, but as it happened with the Normandie, she was never launched due to the outbreak of WW1 . Two of her completed twin turrets, however, were used as naval batteries. They were emplaced in Cap Cépet outside Toulon circa 1928, to guard the approaches of this historic anchorage of the French fleet.

One of the reutilised 340mm twin turrets at Cap Cépet after the war

As France was about to capitulate, a sizeable naval contingent including the MF Bretagne and MF Provence sailed out of Toulon to join the rest of the French fleet anchored at harbour in Mers-El-Kebir, Algeria. After a tense standoff, and a rejected ultimatum, the Royal Navy attacked the French fleet by air and sea in May 1940. This tragic event happened to prevent the warships from falling into German hands, a naval action named Operation Catapult : it remains controversial and divisive to this day. The Bretagne took the brunt of 3 full salvos from the Allied fleet during the battle, the last one successfully penetrating her magazine, and causing a massive explosion. She sank in less than 10 minutes, claiming the life of 977 men – the greatest part of the 1277 French Navy seamen who died on that day.

The MF Bretagne’s magazine explodes in Mers-El-Kebir.

The Provence also started taking water, and eventually settled in the bottom of the harbour. It was however re-floated after the attack, and sailed back to Toulon where it joined the now “neutral” Vichy Navy. In November 1942, she was scuttled by its French crewmen as an act of sabotage, following the Germans assuming full control of the Vichy area. The Cap Cépet battery was also sabotaged in the same action. In the aftermath of the Vichy takeover, Italian occupying forces moved into Toulon, and managed to re-float the Provence from the sea again – just enough to salvage her armaments and other useful components. They then proceeded to utilise the reclaimed barrels from the risen Provence to repair the damaged naval battery at Cap Cépet. As for the poor battleship? She was soon after scuttled, and sank – for the third time in as many years !! – as a blockship in Toulon harbour. She would be raised one last time in 1949, upon which she was broken up for scrap. I don’t recall hearing of another warship having sunk, and re-floated three times.

sudwall quincy 34 cm
A narrow escape for the USS Quincey during Operation Dragoon
sudwall quincy 34 cm 2
The shell could have been fired from the Cap Cépet 340mm battery

But what about the third ship of the class, MF Lorraine? Well the outbreak of the war found Lorraine in Alexandria among a contingent of other French and British warships, where it briefly participated in combined operations against Italian positions in Bardia, Libya, in the North African theatre during June 1940. France soon fell, however, prompting her captain to come to an agreement with the British in Alexandria : To de-militarise, and intern the French ships at port, and so to remain neutral for the duration of hostilities. However this hiatus changed as soon as the Germans occupied the Vichy area in November 1942. The Lorraine instantly joined the navy of the Free French, and after a long refit at the recently liberated port of Oran, Algeria, she joined the Allied fleet on time for Operation Dragoon, the French/American invasion of Southern France that began on the 15th of August 1944.

LORRAINE 1944 8 devant St mandrier (1)
The Lorraine shelling Cap Cépet in August 1944

Joined by an old classmate (USS Nevada, an American Super-Dreadnought launched only few months apart back in 1913), and supported by other warships as well as medium and fighter bombers of the US Tactical Air Force, Lorraine began pouring fire upon Toulon and its defences. For 6 days straight, her 340mm twin turrets traded volleys with her sister 340mm twin turrets based at Cap Cépet (affectionately nicknamed “Big Willie”), before the naval battery on the ground was finally silenced.. and this is how these proud 340mm guns that came out of the same foundry, ended up fighting each other.

34 cm cap cepet 5
Cap Cépet after the bombardment, circa 30 August 1944

The end of the war

And whatever happened to Batterie Plouharnel? Well after the Normandy landings, the Allies attempted to assault the heavily fortified Lorient Submarine Base, which by that time had resisted heavy aerial bombing unscathed. They were unsuccessful : its garrison lasted to the bitter end, finally surrendering on May the 10th 1945. The well defended Plouharnel battery lasted until March 1945, when it was captured after a prolonged artillery bombardment. Both sites were used by the French army after the war, and today they are open to the public, a highly recommended visit in case you find yourselves in Bretagne. I have heard that the some of the guns of Plouharnel (minus the carriages) can still be seen rusting away from the sea in a nearby French army depot, although I haven’t seen these with my own eyes.

Today, the era of Super Dreadnoughts and railroad guns is long gone, as modern navy and artillery doctrines are based on mobility and precision. But the story of the French 340mm naval guns remains an amazing wartime tale from the time when brute firepower was a key component of naval and land operations.


  1. Axis History Forum
  7. Battleship Lorraine
  8. Operation Dragoon
  9. Battleship Bretagne
  10. 340mm/45 Modèle 1912 gun

  11. Battleship Normandie
  12. Battleship Provence
  13. Operation Catapult

All colour photos are © explorabilia. All black and white photos/videos are in the public domain, as far as I am aware, however I have cited all sources above.

  • A short version of this story has appeared at .Special thanks to Pierre Cosmidis for hosting my article.


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