Battle of Muros Bay The Battle of Muros Bay ( Spanish : " Batalla de Muros " ) took place on 25 July 1543 , during the Italian War of 1542 – 1546 , between the French fleet under Jean de Clamorgan , Lord of Soane and the Spanish fleet commanded by Don Álvaro de Bazán , 1st Marquis of Viso , father of Don Álvaro de Bazán , 1st Marquis of Santa Cruz , who was also present at the battle being no more than 18 years old . This battle is considered to be the first big Atlantic naval battle . Background . In 1541 , Francis I of France violated the Truce of Nice and again declared war on Spain , allied with the Ottoman Empire , Denmark and Sweden . Because of this he prepared to enlist an army to fight the Spanish and English navies . The King himself went to the port of Le Havre to oversee the preparations for repelling any English attack . Meanwhile , Vice Admiral De Bury instructed the assembly of a second fleet to attack Spain , he enlisted in the ports of Bayonne and Bordeaux , as at this time the Spanish presence in the Bay of Biscay was very small . The Emperor Charles , fearing action in these waters , designated Don Álvaro de Bazán , to proceed to the Bay of Biscay and assemble a fleet to try to prevent the French attack . Don Álvaro formed a fleet of vessels from Guipuzcoa and Vizcaya , stationing his operations base outside the port of Laredo , within reach of attacking both the French and Cantabrian coast . Don Álvaro was ordered to transport a body of infantry to Flanders , so he had to split the fleet , and fifteen of their ships made the transportation of troops to the city of Bruges , where the infantry was landed at the end of June . Just then , the French finished their preparations , so that with thirty ships , which had been reinforced with 550 specially chosen arquebusier s , it sailed from the port of Bayonne due west to attack the Spanish coast . Although the French fleet had been enlisted by Vice - Admiral De Burye , it was at the time under the command of France ' s greatest seaman , Jean de Clamorgan . The French fleet , on course to approach the coasts of Galicia , captured two Spanish merchant ships , an error which alerted the Governor at the time , Don Sancho de Leyva , who immediately sent emissaries to Bazán warning of the presence of the fleet and its course . Bazán , having been detached from his army and especially the soldiers sent to Flanders at that time , was doing his best to finish fitting out his ships , as he only had at his disposal a few thousand soldiers . Reading the messages of Leiva , he sent for reinforcements , and was quickly reinforced with 500 arquebusiers . On 10 July , the French fleet passed through the waters of Laredo . Thinking that there were no Spanish ships in the area , looted the villages of Lage , Corcubión and more ports found on course , arriving at Cape Finisterre , finally throwing her anchor out at Muros where they demanded a ransom in exchange for not scorching the city . Given the sensitivity of the situation , sailing as fast as he could to get to Muros in as short a time as possible and catch the French off guard . The Battle . The French remained at anchor in front of Muros when the fleet of the Marquis of Viso came over to them at full speed . He only had 16 ships , which were all that he could enlist and equip , but were , apparently , the largest available at the time , giving him a certain advantage over the 25 French ships . As it was 25 July , the Festivity of St . James , " Patrón de España " , Bazán harangued his troops by pointing out that it was impossible for the Spanish to lose a battle on this particular day . The Spanish troops attacked with such a raging fervour , that the French , were overwhelmed in a short time . Don Álvaro turned to aim his flagship against the French Admiral which was positioned next to the corsair Hallebarde , he fought bitterly against them both with such a raging fury , as there were over a hundred men who were still , hors de combat in the Spanish ship . Seeing as the enemy had the advantage , Don Álvaro took advantage of a gust of wind which gave him the momentum necessary to charge Clamorgan ' s ship with such force and skill that he managed to sink it . Once he had sunk Clamorgan ' s ship , Don Álvaro then turned his attentions solely to Hallebarde ' s ship , which was finally boarded and captured . Aftermath . Although the fighting was fierce , lasting a total of just under two hours , at the end of which the French were completely defeated . Of the 25 ships that made up the French fleet , only one escaped . The French casualties exceeded 3 , 000 , but the Spanish a further 800 , of which only 300 were killed . The news of the victory reached the ears of the Emperor and his son , Prince Philip , who were satisfied with the great victory obtained by the Marquis of Viso . With the defeat of the fleet , the French , no longer posed a threat to the coastal towns of northern Spain and the Spanish obtained complete control of the Cantabrian Sea .