Following this campaign, morale and prestige swung England's way in the border region between English-occupied Gascony and French-ruled territory, providing an influx of taxes and recruits for the English armies.

Ralph, Earl of Stafford, had sailed for Gascony in February 1345 with an advance force and, following conventional practice, laid siege to two French strongholds.

By this time the French had diverted their main effort to the south west, under the overall command of John, Duke of Normandy, the son and heir apparent of King Philip VI of France.

The French army started to disintegrate: men were unpaid, even unfed; there was a lack of fodder for the horses; desertion was rife; and troops were selling their equipment.

When an English army had campaigned on the continent earlier in the war it had operated in northern France, causing the Gascons to largely rely on their own resources; they had been hard pressed as a consequence.

Fortifications were also constructed at transport choke points, to collect tolls and to restrict military passage; fortified towns grew up alongside all bridges and most fords over the many rivers in the region.

If they wished to remain in one place for any length of time, as was necessary to besiege a castle, then access to water transport was essential for supplies of food and fodder and desirable for such items as siege equipment.

[23] Derby was given a high degree of autonomy, for example his strategic instructions were: "si guerre soit, et a faire le bien q'il poet" (... if there is war, do the best you can ...).

South-western France was encouraged to rely on its own resources, but as the Truce of Malestroit, signed in early 1343, was still in effect, the local lords were reluctant to spend money, and little was done.

Bad weather forced his fleet of 151 ships to shelter in Falmouth for several weeks en route, finally departing on 23 July.

The Gascons captured the large, weakly garrisoned castles of Montravel and Monbreton on the Dordogne in early June; both were taken by surprise and their seizure broke the tenuous Truce of Malestroit.

The few French troops in the region not garrisoning their fortifications immobilised themselves with sieges: of Casseneuil in the Agenais; Monchamp near Condom; and Montcuq, a strong but strategically insignificant castle south of Bergerac.

There was a further week's delay while the King and his council debated what to do, by which time it proved impossible to take any action with the main English army before winter.

[34] On 9 August 1345 Derby arrived in Bordeaux with 500 men-at-arms, 1,500 English and Welsh archers, 500 of them mounted on ponies to increase their mobility,[10] and ancillary and support troops, such as a team of 24 miners.

The capture of the town, which had good river supply links to Bordeaux, would provide the Anglo-Gascon army with a base from which to carry the war to the French.

[48] Derby consolidated and reorganised for two weeks, left a large garrison in the town and moved north to the Anglo-Gascon stronghold of Mussidan in the Isle valley with 6,000–8,000 men.

[53] The French encampment was divided in two, the majority of the soldiers camped close to the river between the castle and village while a smaller force was situated to prevent any relief attempts from the north.

[54] The chronicler Froissart tells an improbable tale that a soldier attempting to reach the English lines with a letter requesting help was captured and returned to the castle via a trebuchet.

[54] After a night march Derby attacked the French camp on 21 October while they were at dinner, taking them by surprise and causing heavy initial casualties.

[53] There were reports of the French army disintegrating: men unpaid, even unfed; lack of fodder for the horses; desertion; troops selling their equipment.

Despite heavily outnumbering the Anglo-Gascon force the Duke of Normandy retreated to Angoulême and disbanded his army, possibly because the French had run out of funds.

Frequently Derby negotiated trade concessions or privileges with towns, or reinstated previous ones, to encourage them to open their gates to the English forces.

The towns could more readily participate in the lucrative export trade through Bordeaux if under English rule, and Derby's performance lessened their fear of French retribution.

A letter from a committee of French garrison commanders sent to Philip VI in November claimed that towns were defecting to the English on a "daily" basis, and to Anglo-Gascon forces of trivial size.

Stafford marched on the vitally important town of Aiguillon, which commanded the junction of the Rivers Garonne and Lot, "the key to Gascony",[69] in late November.

Towns throughout south-west France embarked on urgent and expensive programmes to repair, improve or in some cases build from scratch their fortifications.

In the border region morale and, more importantly, prestige had decidedly swung England's way following this campaign, providing an influx of taxes and recruits for the English armies.

[38] In October 1345 Northampton commenced his campaign in northern Brittany, but it fizzled out in a series of failures to capture French-held Breton towns.

A large French army, "enormously superior" to any force Derby could field,[88] assembled early in the campaigning season under the Duke of Normandy and marched up the Garonne valley.

[95] The areas facing Derby were left effectively defenceless,[96] and he sent local Gascon forces to besiege the few major strongholds in the region still held by the French.