He then returned to England, where forces were being collected, and was ready to set out again for Guienne in command of them at the beginning of November. He did not, however, actually set sail until the beginning of the new year, 5 Jan. 1367. He landed in Brittany, and marched through Poitou and Saintogne to Bordeaux, and thence to Dax on the Adour, whither the Black Prince had already advanced with his army on the march to invade Spain. Lancaster was appointed captain of the vanguard, and led the first division of the army across the Pyrenees, through the pass of Roncesvalles, 20 Feb. 1367. The English force traversed the kingdom of Navarre, and, entering Castilian territory, occupied Salvatierra, and thence advanced towards Vittoria. During this march Tello, the brother of Henry of Trastamare, made an unexpected attack on Lancaster’s camp in the early morning. The duke appears to have acted with presence of mind, drawing up his men in a good position to resist the enemy; but a detachment of his troops was destroyed almost to a man. The hostile armies lay in sight of each other for some days, when the Black Prince, straitened for provisions, suddenly retreated, and crossing the Ebro, took up a position under the walls of Logroño. Henry followed, and posted himself at Najera. On 2 April the English broke up their camp, and advanced to Navarete, and the next day the armies met between that place and Najera. The vanguard of the Castilians was led by Bertrand du Guesclin and the Marshal d’Audrehem, and was opposed by the division under Lancaster and Sir John Chandos. Froissart describes the duke as taking the lead in the first onslaught. The English were here victorious; Du Guesclin was taken prisoner; and Lancaster coming to the assistance of his brother in his struggle with the main body of the enemy, the battle was won. The victory of Najera restored Pedro to his throne, but brought no advantage to the English. They occupied Burgos for some three weeks, and then went into quarters at Valladolid, awaiting the fulfilment of Pedro’s engagements. He, however, showed no readiness to discharge his debts, sickness broke out, and the mortality was so great that scarcely a fifth of the army is said to have survived. The Black Prince himself was stricken; Henry, who had escaped into France, was threatening Aquitaine; and a speedy retreat from Spain became imperative. This was safely effected, and the prince and Lancaster reached Bordeaux early in September, Lancaster returning thence to England.
Lancaster was appointed captain of the vanguard, and led the first division of the army across the Pyrenees, through the pass of Roncesvalles, 20 Feb. 1367. The English force traversed the kingdom of Navarre, and, entering Castilian territory, occupied Salvatierra, and thence advanced towards Vittoria. During this march Tello, the brother of Henry of Trastamare, made an unexpected attack on Lancaster’s camp in the early morning. The duke appears to have acted with presence of mind, drawing up his men in a good position to resist the enemy; but a detachment of his troops was destroyed almost to a man. The hostile armies lay in sight of each other for some days, when the Black Prince, straitened for provisions, suddenly retreated, and crossing the Ebro, took up a position under the walls of Logroño. Henry followed, and posted himself at Najera. On 2 April the English broke up their camp, and advanced to Navarete, and the next day the armies met between that place and Najera. The vanguard of the Castilians was led by Bertrand du Guesclin and the Marshal d’Audrehem, and was opposed by the division under Lancaster and Sir John Chandos. Froissart describes the duke as taking the lead in the first onslaught. The English were here victorious; Du Guesclin was taken prisoner; and Lancaster coming to the assistance of his brother in his struggle with the main body of the enemy, the battle was won. The victory of Najera restored Pedro to his throne, but brought no advantage to the English. They occupied Burgos for some three weeks, and then went into quarters at Valladolid, awaiting the fulfilment of Pedro’s engagements. He, however, showed no readiness to discharge his debts, sickness broke out, and the mortality was so great that scarcely a fifth of the army is said to have survived. The Black Prince himself was stricken; Henry, who had escaped into France, was threatening Aquitaine; and a speedy retreat from Spain became imperative. This was safely effected, and the prince and Lancaster reached Bordeaux early in September, Lancaster returning thence to England.
After his marriage John to [[Constance of Castile]], the daughter of the exiled [[Peter of Castile|Pedro I]],{{sfn|Walker|2008}} Gaunt assumed the claim officially from 29 January 1372 the title of King of Castile and León, and insisted his fellow English nobles henceforth address him as “my lord of Spain”.<ref>Plea Rolls of the Court of Common Pleas; National Archives; CP 40/541; year 1396. [http://aalt.law.uh.edu/AALT6/R2/CP40no541a/aCP40no541afronts/IMG_0140.htm Several entries, as Duke of Aquitaine & Lancaster; and as King of Castile and Duke of Lancaster]</ref> He [[Impalement (heraldry)|impaled]] his arms with those of the Spanish kingdom. From 1372, John gathered around himself a small court of refugee Castilian knights and ladies and set up a Castilian [[chancery (medieval office)|chancery]] that prepared documents in his name according to the style of [[Peter of Castile]], dated by the Castilian era and signed by himself with the Spanish formula “Yo El Rey” (“I, the King”).{{sfn|Sumption|2009|pp=122–123}} He hatched several schemes to make good his claim with an army, but for many years these were still-born owing to lack of finance or the conflicting claims of war in France or with Scotland.{{cn|date=November 2025}}
After his marriage John to [[Constance of Castile]], the daughter of the exiled [[Peter of Castile|Pedro I]],{{sfn|Walker|2008}} Gaunt assumed the claim officially from 29 January 1372 the title of King of Castile and León, and insisted his fellow English nobles henceforth address him as “my lord of Spain”.<ref>Plea Rolls of the Court of Common Pleas; National Archives; CP 40/541; year 1396. [http://aalt.law.uh.edu/AALT6/R2/CP40no541a/aCP40no541afronts/IMG_0140.htm Several entries, as Duke of Aquitaine & Lancaster; and as King of Castile and Duke of Lancaster]</ref> He [[Impalement (heraldry)|impaled]] his arms with those of the Spanish kingdom. From 1372, John gathered around himself a small court of refugee Castilian knights and ladies and set up a Castilian [[chancery (medieval office)|chancery]] that prepared documents in his name according to the style of [[Peter of Castile]], dated by the Castilian era and signed by himself with the Spanish formula “Yo El Rey” (“I, the King”).{{sfn|Sumption|2009|pp=122–123}} He hatched several schemes to make good his claim with an army, but for many years these were still-born owing to lack of finance or the conflicting claims of war in France or with Scotland.{{cn|date=November 2025}}
