Well informed about the Franco-Breton manoeuvres, the English surprised them at anchor.
Unprepared and confronted by a superior fleet, all the French and Breton ships cut their anchor cables and spread their sails.
By accident, about 300 guests, including some women, were visiting the Breton flagship Marie la Cordelière when it was attacked.
In the hurry, Hervé de Portzmoguer, the captain of the ship, could not disembark them and the crew was thus reinforced by those "involuntary" combatants who, however, fought bravely.

The two main ships (Marie la Cordelière and Petite Louise) faced the enemy to cover the retreat of the rest of the fleet to the port of Brest.
Under English fire, Marie la Cordelière— at 1,000 tons, one of the largest of her time—sailed towards the Regent, with 600 Tons  the largest and most powerful ship in the English navy.
The Sovereign and the Mary James rushed to rescue the Regent and surrounded the Cordelière, while the superior fire of the Mary Rose badly damaged the Petite Louise which was forced to retreat.
The Cordelière remained alone among the English fleet, with the exception of the small Nef-de-Dieppe which harassed the English ships.
The Cordelière's cannons dismasted both Sovereign and Mary James which became ungovernable and drifted in the Iroise Sea.

Hervé de Portzmoguer, also known as "Primauguet", the Breton captain of the Cordelière ordered the assault of the Regent.
Grappling hooks were thrown and the two ships were tied together.
The seamen of the Marie-la-Cordelière rushed on the Regent's deck which was constantly being reinforced by English ships transferring their crews on the Regent.
The little Nef-de-Dieppe manoeuvered skillfully to bombard these new assailants.
The deck of the Regent was covered by blood when, suddenly, the Cordelière exploded.
The flames spread to the Regent and both ships sank.
The crews of both ships were almost entirely annihilated.
Only 20 wounded Breton sailors out of 1,250 were saved from the Cordelière and 60 out of 460 English from the Regent.
Howard was devastated by the death of Thomas Knyvet, commander of the Regent, and vowed "that he will never see the King in the face till he hath revenged the death of the noble and valiant knight, Sir Thomas Knyvet."

Over the next two days, with the French fleet in Brest, the English fleet captured or destroyed thirty-two French vessels and recovered the valuable French anchors before returning to England.
As a result of the engagement Sir Edward Howard was made Lord High Admiral by Henry VIII.
Well informed about the Franco-Breton manoeuvres, the English surprised them at anchor. Unprepared and confronted by a superior fleet, all the French and Breton ships cut their anchor cables and spread their sails. By accident, about 300 guests, including some women, were visiting the Breton flagship Marie la Cordelière when it was attacked. In the hurry, Hervé de Portzmoguer, the captain of the ship, could not disembark them and the crew was thus reinforced by those "involuntary" combatants who, however, fought bravely.
The two main ships (Marie la Cordelière and Petite Louise) faced the enemy to cover the retreat of the rest of the fleet to the port of Brest. Under English fire, Marie la Cordelière— at 1,000 tons, one of the largest of her time—sailed towards the Regent, with 600 Tons  the largest and most powerful ship in the English navy. The Sovereign and the Mary James rushed to rescue the Regent and surrounded the Cordelière, while the superior fire of the Mary Rose badly damaged the Petite Louise which was forced to retreat. The Cordelière remained alone among the English fleet, with the exception of the small Nef-de-Dieppe which harassed the English ships. The Cordelière's cannons dismasted both Sovereign and Mary James which became ungovernable and drifted in the Iroise Sea.
Hervé de Portzmoguer, also known as "Primauguet", the Breton captain of the Cordelière ordered the assault of the Regent. Grappling hooks were thrown and the two ships were tied together. The seamen of the Marie-la-Cordelière rushed on the Regent's deck which was constantly being reinforced by English ships transferring their crews on the Regent. The little Nef-de-Dieppe manoeuvered skillfully to bombard these new assailants. The deck of the Regent was covered by blood when, suddenly, the Cordelière exploded. The flames spread to the Regent and both ships sank. The crews of both ships were almost entirely annihilated. Only 20 wounded Breton sailors out of 1,250 were saved from the Cordelière and 60 out of 460 English from the Regent. Howard was devastated by the death of Thomas Knyvet, commander of the Regent, and vowed "that he will never see the King in the face till he hath revenged the death of the noble and valiant knight, Sir Thomas Knyvet."
Over the next two days, with the French fleet in Brest, the English fleet captured or destroyed thirty-two French vessels and recovered the valuable French anchors before returning to England. As a result of the engagement Sir Edward Howard was made Lord High Admiral by Henry VIII.
Battle of Saint-Mathieu