Battle of Sandwich ( 1217 ) In the Battle of Sandwich on 24 August 1217 a Plantagenet English fleet commanded by Hubert de Burgh attacked a Capetian French armada led by Eustace the Monk and Robert of Courtenay . The English captured the French flagship and most of the supply vessels , forcing the rest of the French fleet to return to Calais . The naval battle took place off Sandwich , Kent on the English coast during the First Barons ' War . The French fleet was attempting to bring supplies to Prince Louis , later King Louis VIII of France , whose French forces held London at that time . The English vessels attacked from windward , seizing Eustace ' s ship , making Robert and the knights prisoner and killing the rest of the crew . Eustace , a notorious pirate , was executed after being taken prisoner . The battle convinced Prince Louis to abandon his effort to conquer England and the Treaty of Lambeth was signed a few weeks later . Background . Eustace the Monk once belonged to a monastic order , but he broke his vows and became a pirate along with his brothers and friends . His early successes at this endeavor attracted many lawless men and his pirates became a menace to shipping in the English Channel . The English opponents of Eustace credited the man with " diabolical ingenuity " . From 1205 to 1208 , Eustace worked for King John I of England . With the English sovereign ' s blessing he seized the Channel Islands and was allowed to hold them for John , while using Winchelsea as his English base . In 1212 , Eustace switched his allegiance to France and was chased out of England . The year 1215 saw his ships transporting war engines to the English barons who opposed John . When Prince Louis sailed for London , he traveled in Eustace ' s fleet . It was thanks to Eustace ' s help that Louis was able to quickly capture London and the Cinque Ports . After his lieutenants were badly defeated at the Battle of Lincoln on 20 May 1217 , Prince Louis raised his siege of Dover Castle and retired to London . Signalling his willingness to negotiate an end to the struggle , he agreed to meet at Brentford with adherents of the boy - king Henry III of England . The victor of Lincoln , William Marshal , 1st Earl of Pembroke and Louis came close to an agreement . However , in order to pardon the bishops who had gone over to Louis ' cause , Pope Honorius III ' s acquiescence was required . Since this was not possible without a long journey to Rome , the negotiations broke down . Louis received the news that reinforcements and supplies would soon arrive from France . Encouraged , he resolved to fight on . Battle . On 24 August , in clear weather , the French fleet set out from Calais . Though the ships were equipped by Eustace the Monk , command of the knights and soldiers was held by Robert of Courtenay . The wife of Prince Louis , Blanche of Castile was also an important organizer of the relief effort . Opposing the French was Philip d ' Aubigny , commander of the southeastern coast . The Earl of Pembroke had arrived at New Romney on 19 August and summoned the sailors of the Cinque Ports . The English mariners complained bitterly of bad treatment at the hands of King John , but Pembroke convinced them to fight with the promise of great spoils should they defeat the French . Eustace ' s own vessel , the " Great Ship of Bayonne " led the French squadron . Robert de Courtenay held the top command while Eustace served as his deputy . Ralph de la Tourniele and William des Barres were third and fourth in command , respectively . All told , there were 36 knights on the flagship . The next three troopships were commanded by Mikius de Harnes , William V of Saint - Omer , and the Mayor of Boulogne . Altogether , the first four ships , including the flagship , contained between 100 and 125 knights . Men - at - arms manned the remaining six troopships . There were 70 smaller vessels which carried supplies . All eleven troopships were overloaded , particularly the flagship which carried a large trebuchet and horses destined for Prince Louis . The English ships were generally smaller than the French , except for a substantial cog ( ship ) provided by the Earl of Pembroke , who was persuaded to stay ashore . As justiciar , Hubert de Burgh claimed leadership of the fleet , which included between 16 and 18 large ships and 20 smaller vessels . All told , there were no more than 40 English ships . A bastard of King John , Richard Fitz - John commanded one ship . The English , who had recovered Sandwich from Louis ' forces , determined to let the French armada pass by before attacking . When the French sailed past Sandwich , de Burgh ' s fleet issued from the port . The French fleet , which sailed in close order toward the Thames estuary , held the windward position at first . De Burgh ' s ship , which was in the lead , lunged at the French in a feint attack , but veered away when threatened . Against the advice of his admiral Eustace , the overconfident Robert of Courtenay ordered the French to attack . As the French shortened sail , the English ships gained the windward position and attacked . Meanwhile , de Burgh ' s flagship sailed independently to attack the French from the rear , eventually capturing two French vessels . Aided by their upwind position , the English archers inflicted considerable execution on the enemy sailors and soldiers before the French bowmen were able to effectively reply . The English also opened pots of lime which blew in the faces of the French . Early in the battle , the French flagship engaged Richard Fitz - John ' s ship . As more English ships came up , they joined the fight against the flagship , while the other French ships maintained their tight formation , but failed to assist their flagship . Pembroke ' s cog and Fitz - John ' s ship grappled Eustace ' s flagship , one on each side . After a one - sided melee , Robert of Courtenay and the French knights were captured for ransom , while the French sailors and common soldiers were massacred . Eustace , dragged from his hiding place in the bilge , offered to pay 10 , 000 marks as ransom . Though his very high price was tempting , Fitz - John and the other English leaders considered Eustace a turncoat because of the pirate ' s employment by King John . Marked for execution by the enraged English , Eustace was tied down and a man named Stephen Crabbe struck off his head with one blow . With their flagship taken , the French fleet headed back to Calais . Encouraged , the English attacked , using ramming , grappling , and rigging - cutting to disable the enemy vessels . The nine surviving troopships got away , but most of the smaller vessels fell prey to the English mariners . As few as 15 ships escaped from the rampaging English . The French troopships owed their deliverance to their train of supply vessels because the English turned aside to plunder the smaller craft . The French sailors were slaughtered or thrown into the Channel , except for two or three men on each captured vessel who were spared . Result . A large part of the loot passed to the English sailors while some was used to set up the Hospital of Saint Batholomew at Sandwich . Historian Thomas B . Costain calls the English victory decisive . Before the battle Prince Louis was short of supplies . With the English in control of the Channel , Louis was totally cut off from his French logistic base . His allies among the English barons craved a settlement and amnesty for themselves . Peace was signed on 12 September at Kingston upon Thames . Prince Louis formally renounced his claims to the English crown in return for being allowed an unmolested departure from England . A few of Henry ' s supporters held out for unconditional surrender , but the Earl of Pembroke successfully argued for the more moderate terms . In return for Henry III ' s pardon , the barons who had joined Louis were made to pay the French prince 10 , 000 marks to expedite his withdrawal . Prince Louis left Dover before the end of the month . References .