 He attended the king in Brabant, serving in September 1339 in the expedition that besieged Cambrai, and in the army that prepared to fight a major battle at Buironfosse that came to nothing, where he and the Earl of Derby held a joint command.On 15 November of the same year he was appointed joint ambassador to Louis I, Count of Flanders and the Flemish estates, to treat for an alliance.After Edward's return to England, Suffolk stayed behind with Salisbury, in garrison at Ypres.