Explosion aboard the cruiser Pluton

On the morning of 13 September 1939, ten days after France declared war on Germany, the minelaying cruiser (PL) Pluton exploded in the harbour of Casablanca in French Morocco. Moored alongside the quay, the ship was unloading naval mines that had been prepared a few days earlier for laying a barrage and which, once that task had been cancelled, had to be disarmed. At around 10.40 a.m. one of them exploded, setting off others. Pluton was torn apart and settled on the bottom of the harbour basin. Some two hundred people were killed, most of them sailors from her crew. It was the first major loss suffered by the French navy, the Marine nationale, in the Second World War, although it was not inflicted by the enemy.

A figure of 215 dead is sometimes given, but only some lists put it that high. French studies based on naval records name 186 members of the ship’s crew killed or missing and about twenty dead among the workers of the port’s technical services, while some English sources give 186 victims in total. It is safest to speak of roughly two hundred dead.

The ship

Pluton was the only ship of her type. She was built in the second half of the 1920s under the fleet expansion programme of 1925, on the model of the British minelayer HMS Adventure. She was more than 150 metres long, could make over 30 knots and was armed with four 138 mm guns. She had no armour at all: she was meant to be fast, not tough. Her mine deck, running almost the full length of the hull, held on rails more than two hundred large moored mines, which were dropped over ramps at the stern. If necessary she could also carry up to a thousand troops. She entered service in 1932 and soon, because of numerous defects and the lack of peacetime work for a minelayer, was converted into a gunnery training ship.

In the spring of 1939, as war drew ever closer, she was transferred to Lorient in Brittany, where a squadron of training ships was being formed. There were even plans to rename her La Tour d’Auvergne in 1940. At the end of August, however, it was decided that she would return to her original role, and most of her training equipment was removed.

The voyage to Casablanca

On 2 September 1939, with general mobilisation already under way in France, Pluton, under the command of Captain (capitaine de vaisseau) Henri Dubois, sailed from Brest for Casablanca with 125 Bréguet mines on board. She was to lay a defensive minefield off this important Atlantic port of the French colonial empire. The French command expected German submarines and surface ships to appear on the routes linking metropolitan France with North Africa, and in the first days of the war the attitude of Italy and Spain was also uncertain. The ship reached Casablanca on 5 September.

The mines were prepared for laying: their pistols were fitted, that is, they were armed. Then the task was cancelled. Sources differ as to when and why. According to some accounts, the order to lay the barrage was issued on 4 September and withdrawn the very next day; according to others, the barrage was to be laid during the night of 12–13 September and the Admiralty cancelled the task on the evening of 12 September. The reasons given are a revised assessment of the threat and unfavourable tidal conditions. What is certain is that the ship was ordered to unload the armed mines ashore, from where they were to go to the naval ammunition depot near Casablanca to be disarmed.

The disaster

Unloading began at around 10.30 a.m. on 13 September. Pluton lay at the Delure quay, in the very centre of the busy port, close to fishing boats, auxiliary minesweepers and submarines. At around 10.40 a.m. flames burst out amidships, between the second funnel and the mainmast, followed by a powerful explosion and, a few seconds later, a second, even more violent one: the first mine had set off others. The blast tore the hull open, destroyed the bulkheads and set fire to several hundred tonnes of fuel. Fragments of the ship and pieces of deck equipment rained down on the quays, crushed the vehicles parked there and, according to accounts, were scattered up to two kilometres away. The roar was reportedly heard a hundred kilometres away, and a column of smoke rose several thousand metres into the sky.

The submarines in the harbour were ordered to put to sea at once, and the port entrance was closed. The wreck heeled over and at around 11.15 a.m. settled on the bottom. The fire spread towards the bow and was put out only in the evening. The blast wave and falling debris sank three fishing boats (Étoile du Matin, Marie Merveilleuse and Sultan) and damaged several auxiliary minesweepers beyond repair.

Captain Dubois was killed. According to French records, 186 of Pluton’s crew were killed or missing and 73 were wounded. Among the workers of the port’s technical services who were helping with the unloading, some twenty were killed or missing and several dozen wounded. The commission that investigated the causes of the disaster concluded that the explosion had been caused by an error in disarming one of the mines. As almost everyone working on it had died, the exact sequence of events was never established.

Silence in the press

The disaster caused no great stir in France. The country was in the first weeks of the war, the press was subject to wartime censorship, and the naval command had no wish to publicise the loss of a ship in an accident. Newspaper reports were terse. The wreck of Pluton lay in Casablanca harbour throughout the war. One gun and some of her equipment were recovered, but breaking up began only in October 1952 and was completed in July 1953.

Significance

The explosion at Casablanca had no effect on the course of the war. Pluton was an auxiliary vessel, and her loss did not significantly weaken the French fleet, which Admiral François Darlan had built up in the 1930s and which was the strongest in Europe after the British. The disaster nevertheless captures well the character of the first weeks of the war in the west. While the September Campaign was being fought in Poland and the French army confined itself to a cautious advance into the Saar, which was soon halted, France was suffering its first casualties not in battle but in accidents and in preparations for a war that had not yet really begun. This period, later called the “Phoney War”, lasted until May 1940.

Casablanca was yet to play an important part in the war. After the fall of France in June 1940 its port came under the authority of the Vichy government, and in November 1942 the French fleet there resisted the American landings during Operation Torch. The battleship Jean Bart and the ships lying in the harbour where Pluton had been lost then fought the United States Navy, before North Africa went over to the Allied side.