the battle, put the English force on 'perhaps' 14 ships. A fleet of 20 vessels is considered a creditable force. Sir Philip Courtenay, Admiral of the West, provided escort with 3 larger fighting ships (large tonnage and archer towers). The English rule in Aquitaine was by then under threat. Since 1370 large parts of the region had fallen under French rule. In 1372, Bertrand du Guesclin lay siege at La Rochelle. To respond to the demands of the Franco-Castilian alliance of 1368, the king of Castile, Henry II of Trastámara, dispatched a fleet to Aquitaine under Ambrosio Boccanegra, assisted by Cabeza de Vaca, Fernando de Peón and Rui Díaz de Rojas. The size of this fleet is also uncertain. According to López de Ayala, it was composed of 12 galleys. Froissart, in his first account, mentioned 40 sailing ships and 13 barges, but later reduced this number to 13 galleys. Quatre Premiers Valois and Chronique des Pays-Bas mention respectively 20 and 22 galleys. Battle On 21 June the English fleet arrived at La Rochelle and the battle began as Pembroke's ships approached the harbour. This lay at the head of an inlet which was partially unnavigable at low water. The first Castilian attacks met strong resistance. The English, despite the inferiority of their numbers, defended themselves vigorously. At dusk, when the tide rose, the two fleets separated. Though they had lost two or four vessels, according to Froissart, the English were not yet defeated. Pembroke then withdrew some way from land, while Boccanegra anchored in front of La Rochelle. The Chronicle Quatre Premiers Valois, unlike López de Ayala and Froissart, implies that only some skirmishes took place on the first day, as Boccanegra would have ordered his galleys to withdraw, reserving them for the main action. According to this chronicle, the anchoring sites were reversed: the English off the town and the Castilians on the open sea. Froissart described a discussion between Pembroke and his men during the night of 21–22 June regarding how to escape the trap. An attempt to escape under the cover of the night was dismissed due to the fear of the Castilian galleys, as well as another to enter La Rochelle because of the low draft of the passage. In the end, the low tide left the English ships aground. Castilian galleys could maneuver freely in shallow water. That gave them a decisive tactical advantage.