IIFC, the French BB Bretagne was destroyed by the RN when it refused to submit to an ultimatum. There was a huge loss of life, so I believe it was a large explosion, yes? Was it the ship magazines? I have had conflicting evidence. Again, IIFC, there were 977 lives lost, and less than 10 survived? Or was it just the fire from three capital ships combined at close range?
Total killed were 36 Officers, 151 Petty Officers and 825 Seaman. It was the combined fire of battleships HMS Barham and HMS Resolution and battlecruiser HMS Hood that destroyed it. Mers-El-Kebir
Two shells from the third British salvo struck Bretagne. One struck underwater below turret 4 and caused a large explosion and massive flooding. The other penetrated the upper belt and protective deck, exploding in an engine room. Many damage control personnel were killed, and shipboard power and communications began to fail. A large explosion shook the ship. The skipper attempted to get Bretagne beached, but she'd been immobilized. Seven minutes after the first hits, two more shells landed. One damaged the foremast and started fires among ready-use ammo. The other shell struck the midships turret, and a massive explosion sent up a sheet of flame stretching from the foremast to the after turrets. The ship was sinking by the stern and listing 40deg as another explosion took place. As the list reached 80deg, there was another explosion. Bretagne capsized and gave a final explosion. I have no doubts that there was a magazine explosion, though it turned out that many crewmen survived in the overturned hull, some surviving trapped for days before they died.