The campaign at sea resumed in September 1338, when a large French and Italian fleet descended on the Channel Islands once again under Robert VIII Bertrand de Bricquebec, Marshal of France. The island of Sark, which had suffered a serious raid the year before, fell without a fight and Guernsey was captured after a brief campaign. The island was largely undefended, as most of the Channel Islands garrison was in Jersey to prevent another raid there, and the few that were sent to Guernsey and Sark were captured at sea. Messengers from the islands were also captured, preventing the English government from discovering what had happened for over a week. On Guernsey, the forts of Castle Cornet and Vale Castle were the only points to hold out. Neither fort lasted very long as both were undermanned and unprovisioned. The garrisons were put to death. A brief naval battle was fought between Channel Islanders in coastal and fishing vessels and Italian galleys, but despite two of the Italian ships being sunk the Islanders were defeated with heavy casualties. Guernsey remained French for sometime, only being relinquished when defending the island became untenable in the aftermath of the battle of Sluys. The next target for Béhuchet and his lieutenant Hugh Quiéret were the supply lines between England and Flanders, and they gathered 48 large galleys at Harfleur and Dieppe. This fleet then attacked an English squadron at Walcheren on 23 September. The English vessels were unloading cargo and were surprised and overwhelmed after bitter fighting, resulting in the capture of five large and powerful English cogs, including Edward III's flagships the "Cog Edward" and the "Christopher". The captured crews were executed and the ships added to the French fleet. A few days later on 5 October, this force conducted its most damaging raid of all landing several thousand French, Norman, Italian and Castilian sailors close to the major port of Southampton and assaulting it from both land and sea. The town's walls were old and crumbling and direct orders to repair it had been ignored. Most of the town's militia and citizens fled in panic into the countryside, with only the castle's garrison holding out until a force of Italians breached the defences and the town fell. The scenes of Portsmouth were repeated as the entire town was razed to the ground, thousands of pounds worth of goods and shipping taken back to France and captives massacred or taken as slaves. The following day militia bands began to harass the French force on the outskirts of the town and the French departed, leaving behind the burning town, which was further damaged by brigands who came to loot before the local authorities could return.