While in Admiral Hawke's fleet, under Captain Richard Howe, Magnanime took part in the 1757 Raid on Rochefort, one of a series of raids designed to draw French troops away from the German front.

The plan to take Rochefort itself was later abandoned but Île d'Aix was captured and in the preceding battle, it was Magnanime's guns that bombarded the island's fort into submission.
The British fleet began its final approach to Basque Roads on 19 September 1757, Île-d'Aix lying some way beyond at the mouth of the Charente estuary.
The island was extremely important to the port of Rochefort because ships of the line were required to load and unload supplies and armaments there, being unable to navigate the shallow river fully laden.
It was expected therefore to be heavily defended.
Although, as Hawke was later to discover, a couple of third rates would be sufficient for the task.

Hawke had formed an advanced squadron, under Sir Charles Knowles, comprising Magnanime, Barfleur, Neptune, Torbay and Royal William, and at around noon he sent these ships on ahead.
 Just after 14:00, as they were approaching the Antioch Passage, between Île d'Oléron and Île de Ré, a French two-decker was sighted, and Magnanime and two other vessels were ordered to pursue.
The squadron was now without a competent pilot, who was aboard Magnanime, and the fleet, Hawke having by this time caught up, had to wait until the three ships returned the following afternoon.
 By this time the wind had dropped and the British were forced to anchor.
 The lack of wind caused further delays and it was not until the fifth attempt that the British finally managed to enter the bay.
On the morning of 23 September, at around 10:00, Knowles' squadron, with Magnanime in the lead, was sent to silence the batteries on Île de Aix.
Howe came within range of the fort at noon but held his fire for a further hour until he had brought Magnanime up within 40 yards (37 m).
Shortly after the second ship, Barfleur arrived, the fort surrendered.
While in Admiral Hawke's fleet, under Captain Richard Howe, Magnanime took part in the 1757 Raid on Rochefort, one of a series of raids designed to draw French troops away from the German front.
The plan to take Rochefort itself was later abandoned but Île d'Aix was captured and in the preceding battle, it was Magnanime's guns that bombarded the island's fort into submission. The British fleet began its final approach to Basque Roads on 19 September 1757, Île-d'Aix lying some way beyond at the mouth of the Charente estuary. The island was extremely important to the port of Rochefort because ships of the line were required to load and unload supplies and armaments there, being unable to navigate the shallow river fully laden. It was expected therefore to be heavily defended. Although, as Hawke was later to discover, a couple of third rates would be sufficient for the task.
Hawke had formed an advanced squadron, under Sir Charles Knowles, comprising Magnanime, Barfleur, Neptune, Torbay and Royal William, and at around noon he sent these ships on ahead.  Just after 14:00, as they were approaching the Antioch Passage, between Île d'Oléron and Île de Ré, a French two-decker was sighted, and Magnanime and two other vessels were ordered to pursue. The squadron was now without a competent pilot, who was aboard Magnanime, and the fleet, Hawke having by this time caught up, had to wait until the three ships returned the following afternoon.  By this time the wind had dropped and the British were forced to anchor.  The lack of wind caused further delays and it was not until the fifth attempt that the British finally managed to enter the bay. On the morning of 23 September, at around 10:00, Knowles' squadron, with Magnanime in the lead, was sent to silence the batteries on Île de Aix. Howe came within range of the fort at noon but held his fire for a further hour until he had brought Magnanime up within 40 yards (37 m). Shortly after the second ship, Barfleur arrived, the fort surrendered.
HMS Magnanime (1748)