The king's wrath at this overthrow of his hopes showed itself in a brutal and impolitic act of vengeance. He was a skilful shipbuilder; and among the many enterprises which the restless genius of Cromwell undertook there was probably none in which Henry took so keen an interest as in his creation of an English fleet. Hitherto merchant ships had been impressed when a fleet was needed; but the progress of naval warfare had made the maintenance of an armed force at sea a condition of maritime power, and the resources furnished by the dissolution of the abbeys had been devoted in part to the building of ships of war, the largest of which, the _Mary Rose_, carried a crew of seven hundred men. The new strength which England was to wield in its navy was first seen in 1544. An army was gathered under Lord Hertford; and while Scotland was looking for the usual advance over the border the Earl's forces were quietly put on board and the English fleet appeared on the third of May in the Firth of Forth. The surprise made resistance impossible. Leith was seized and sacked, Edinburgh, then a town of wooden houses, was given to the flames, and burned for three days and three nights. The country for seven miles round was harried into a desert. The blow was a hard one, but it was little likely to bring Scotchmen round to Henry's projects of union. A brutal raid of the English borderers on Melrose and the destruction of his ancestors' tombs estranged the Earl of Angus, and was quickly avenged by his overthrow of the marauders at Ancrum Moor. Henry had yet to learn the uselessness of mere force to compass his ends. "I shall be glad to serve the king of England, with my honour," said the Lord of Buccleugh to an English envoy, "but I will not be constrained thereto if all Teviotdale be burned to the bottom of hell." Hertford's force returned in good time to join the army which Henry in person was gathering at Calais to co-operate with the forces assembled by Charles on the north-eastern frontier of France. Each sovereign found himself at the head of forty thousand men, and the Emperor's military ability was seen in his proposal for an advance of both armies upon Paris. But though Henry found no French force in his front, his cautious temper shrank from the risk of leaving fortresses in his rear; and while their allies pushed boldly past Chalons on the capital, the English troops were detained till September in the capture of Boulogne, and only left Boulogne to form the siege of Montreuil. The French were thus enabled to throw their whole force on the Emperor, and Charles found himself in a position from which negotiation alone could extricate him. [Sidenote: Growth of Lutheranism.]