On 18 March, the Anglo-French fleet mounted a major attack on the Ottoman defences; "Ocean" joined ten British battleships and one battlecruiser and four French battleships for the operation. The plan called for the battleships to enter the narrows and suppress the fortresses while minesweepers cleared paths in the Ottoman minefields. At the same time, transport ships outside the straits would conduct a demonstration to convince the Ottomans they were going to land troops; the Entente commanders hoped this would tie down the Ottoman mobile guns. The British ships initially succeeded in inflicting heavy damage on the fortresses, but the battleship and then the battlecruiser began taking serious damage from the coastal batteries. The French battleships also began to take damage, and the battleship "Bouvet" struck a mine and exploded. Later in the day, was disabled by a mine in Erenköy Bay. Once it became apparent that the ship could not be saved, all of her surviving crew was taken off by destroyers except for her commanding officer and some volunteers trying to keep her afloat. "Ocean" was sent in to tow her out, but she ran aground during the attempt, and, after freeing herself, found it impossible to take "Irresistible" under tow because of the shallow water, "Irresistible"s increasing list, and heavy enemy fire. "Ocean" then took off the remaining members of "Irresistible"s crew and left the abandoned battleship to her fate; "Irresistible" sank unobserved by Allied forces, at around 19:30.