The year had started with a "huge"[1] French army under John, Duke of Normandy, son and heir of King Philip VI, besieging the strategically important town of Aiguillon in Gascony.

After a five-month siege the French were ordered north to confront the main English army, which on 12 July had landed in Normandy under Edward III of England and commenced the Crécy campaign.

Lancaster took advantage by launching offensives into Quercy and the Bazadais and himself leading a third force on a large-scale mounted raid (a chevauchée) between 12 September and 31 October 1346.

All three offensives were successful, with Lancaster's chevauchée, of approximately 2,000 English and Gascon soldiers, meeting no effective resistance from the French, penetrating 160 miles (260 kilometres) north and storming the rich city of Poitiers.

His force then burnt and looted large areas of Saintonge, Aunis and Poitou, capturing numerous towns, castles and smaller fortified places as they went.

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.

[22] John, Duke of Normandy, the son and heir of Philip VI, was placed in charge of all French forces in southwest France, as he had been the previous autumn.

[27] This reliance was misplaced given the naval technology of the time and the French were unable to prevent Edward III successfully crossing the Channel and landing in the Cotentin Peninsula, in northern Normandy, on 12 July with an army between 12,000 and 15,000 strong.

[27] The English achieved complete strategic surprise and marched south,[28] cutting a wide swath of destruction through some of the richest lands in France and burning every town they passed.

Local English sympathisers in the Agenais under Gaillard I de Durfort blockaded Agen and Porte Sainte Marie and raided into Quercy to the west.

A large detachment of Gascons was split up to reoccupy the French-held territory to the south and west of the Garonne under the overall command of Alixandre de Caumont, in a mopping up operation.

The army of John of Armagnac was diverted to Tulle, which it besieged from mid-November until late December, when the Gascon occupiers surrendered on terms and were taken prisoner; all were ransomed.

[36] Lancaster targeted the rich provincial capital of Poitiers, deep in French-held territory – 160 miles (260 kilometres) north of his starting point.

Leaving a garrison, Lancaster turned back towards Poitiers, covering 20 miles a day and taking the towns of Melle and Lusignan on the way.

During the night the English found a breach in the wall, which had been deliberately created years before to allow easy access from the city to a nearby watermill.

[39] Lancaster was unable to take the royal mint at Montreuil-Bonnin, 5 miles (8 kilometres) west of Poitiers, and marched rapidly back to Saint-Jean-d'Angély.

He made no attempt to hold Poitiers; in the province of Poitou he only left troops at Lusignan, a small town with good walls and a strong, modern castle.

Once back in Saintonge he took control of the Boutonne valley all the way to the sea, including the major port of Rochefort and the well-fortified island of Oléron.

[40] The French were left in control of much of Saintonge: the eastern parts; the larger fortifications such as the province's capital, Saintes, and its strongest castle, Taillebourg; and several strategically important strongholds on the east bank of the Gironde.

The French ability to counter-attack was lost as they concentrated on attempting to defend the host of newly vulnerable locations or on recovering towns captured deep in what had been considered safe territory, as at Tulle.

Lancaster joined it there in the summer of 1347 and was present when Calais fell after an eleven-month siege, securing an English entrepôt into northern France which was held for two hundred years.