In 1439 Hoo was in Lord Talbot's forces in the large expedition into France under Richard Duke of York, and was sent by his commander to the Captain at Mantes and to the Lieutenant at Pontoise, to strengthen the garrison of Vernon. He himself succeeded as Bailiff and Captain of Mantes in 1440 and 1441, until in November of the latter year replacing Neville, Lord Falconbridge as Captain of Verneuil and serving also as Master of Ostel. In January 1442 he went with François de Surienne to propose a scheme to capture the town and fortress of Gallardon: they were to pay for the men-at-arms and archers, and to provide 250 men each to the King's service, but if successful were to have command of the place and the division of the spoils, and Sir Thomas was to be reimbursed his expenses. By July 1442 the scheme had a successful outcome.