“There was absolutely no nuclear fuel aboard and not a single weapon. In fact the submarine was stripped bare,” French Armed Forces Minister Florence Parly added June 13 during a trip to the French naval base of Toulon on the Mediterranean coast to see the damage.

“This was a fire, it was not a nuclear accident,” she added.

The fire broke out at 10:35 a.m. local time at the front of the sub, which was in basin No. 3 in the Missiessy zone of the port. Workmen first noticed smoke on the lower deck.

Sources quoted by French daily Le Monde say the fire seems to have taken in a similar way to that of the Notre Dame Cathedral, with soldering work undertaken a few days before, which may have set something smoldering. The bits of wood and oil inherent to this type of renovation work could have fed the fire.

“Fighting a fire on a submarine is not at all obvious, particularly in very thick smoke,” Parly said after praising the “remarkable work” of both Navy and civilian firefighters who put the fire out in the early hours of June 13.

The French Navy says a fleet of six submarines is necessary so as to have two or three of them permanently at sea to escort the carrier fleet, gather intelligence and deploy personnel. But after this fire, of the six Rubis-class submarines that entered service between 1983 and 1993, only three are available today. The first of class, the Rubis, is also under maintenance, while the Saphir was decommissioned in June 2019. Parts of the Saphir could be made available to repair damage to the Perle.

The Perle has been operational since July 7, 1993, and the ongoing renovations were designed to prolong its life until 2030.

It will take at least a month of investigations to understand whether the steel hull is so damaged as to make the sub unusable, according to Naval Group officials. The steel can withstand the intense heat of a fire for a certain number of hours, but engineers will have to check whether it has maintained the elasticity required to withstand wide variations in pressure when underwater.

The Rubis class will be replaced by six Suffren-class submarines, the first of which was launched July 12, 2019, but is still undergoing tests by the Navy and will not enter service until next year.

The 73.6-meter-long, 2,500-ton Rubis-class subs are the most compact nuclear-powered attack submarines in the world.