Eustace the Monk - Battle of Dover
In 1217 the French were besieging Dover Castle - they tried in May to bring a convoy to resupply the besiegers but were forced back by an English squadron under Philip d'Aubigny, in August they tried again.
NAM Rodger "As the French passed along the coast the English sailed from Sandwich, initially close hauled to pass astern of the French. Eustace the Monk, the French commander, interpreted this as an attempt to avoid battle and attack Calais (which was well fortified) while they were absent. In fact de Burgh's [English commander] object was to gain the weather gage; as soon as he was astern and to windward of the the French, the English ships bore up and attacked. It looks as though the French squadron was straggling, and Eustace's ship, heavily laden with a trebuchet, was certainly astern of the rest. Thus the English were able to defeat and capture the enemy fleet in detail. This battle was fought at sea under sail, but probably in the sheltered waters of the Downs or even further North off Ramsgate, rather than off Dover, the name conventionally given to it. Fought underway in an age when when naval battles were usually stationary, it displays a precocious grasp of naval tactics by Hubert de Burgh which was hardly equalled by any other English admiral before the sixteenth century. It is one of the most decisive medieval naval battles in northern waters, for it effectively ended the French attempt to conquer England.."