There was at least one arranged deed of arms connected with the campaign, at Entenza or Entenca in 1387, just north of the Portuguese border on the road between Santiago and Oporto, between Sir John Holland and Sir Reginald de Roye of France.
John of Guant:
king of Castile and Leon, duke of Aquitaine and Lancaster, earl of Derby, Lincoln, and Leicester, seneschal of England
English leave Plymouth, July 9, 1386
En route, they relieve the English garrison of Brest, under attack by the French.
English land at Corunna: July 25, 1386
Soon after, they went to Santiago, which surrendered on terms.
The army was advancing gaily in battle array towards the town of St. Jago: when about two French leagues from the place, they were met by a long procession of the clergy, bearing relics, crosses and streamers, and crowds of men women and children, and the principal inhabitants carrying the keys of the town, which they presented on their knees, with much seeming good will, to the duke and duchess, (but whether it was feigned or not, I cannot say) and acknowledged them for their king and queen. Thus they entered the town of St. Jago, and rode directly to the church of St. James, where the duke, duchess, their children and attendants, kneeling, offered up their prayers to the holy body of St. James, and made rich gifts at the altar. It was told me that the duke, duchess, and the ladies, Constance and Philippa, were lodged in the Abbey, and there held their court. Sir John Holland and Sir Thomas Moreaux, with their ladies, were lodged in the town: the other barons and knights as they could, and the men at arms on the plains round the town. Those who could not find houses, built themselves huts covered with boughs, of which there were plenty in the country, and made themselves comfortable with what they could get. Meat and strong wines were in abundance; of which the archers drank so much that they were for the greater part of their time in bed drunk; and very often, by drinking too much new wine, they had fevers, and in the morning such headaches as to prevent them from doing anything the remainder of the day; for it was now the vintage.
(Froissart, Johnes tr.)
The marriage of the King of Portugal and Philippa, daughter of the Duke of Lancaster February 14, 1387
A deed of arms between Sir John Holland and Sir Reginald de Roye: Entença, after March, 1387
A strategem leads to the fall of Ferrol in Galicia
A battle at the barriers at Noya
After the beginning of April, 1387, Anglo-Portuguese army invades Leon
There had not fallen any rain or dew since the beginning of April, so that the whole country was burnt up. The English ate plentifully of grapes wherever they found them; and, to quench their thirst, drank of the strong wines of Castille and Portugal: but the more they drank the more they were heated; for this new beverage inflamed their livers, lungs, and bowels, and was in its effect totally different from their usual liquors. The English, when at home, feed on fresh meats and good rich ale, which is a diet to keep their bodies wholesome; but now they were forced to drink hard and hot wines, of which they were not sparing, to drown their cares. The early part of the night is warm, from the great heat of the day, but, toward sun-rise, it is very cold, which afflicted them sorely; for they slept without covering, and quite naked, from the heat of the weather, and the wine, so that when morning came they were chilled by the change of air, which checked all perspiration, and flung them into fevers and fluxes, so as to carry them off instantly to their graves. Thus died very many of the barons and knights, as well as of the lower ranks; for these disorders spared none.
(Froissart, Johnes tr.)
Between June and July of 1387, John of Gaunt negotiated a preliminary exit strategy, the Treaty of Trancoso. This was finalized as the Treaty of Bayonne in July of 1388.
Gaunt played a weak hand well. He and Constanza gave up their claims to the throne of Castile in return for a large lumps sum payment, a generous annuity, and marriage of their daughter Catherine to the heir of the throne of Castile.