 As the Dutch approached with the aim of surrounding the city of Antwerp, the Cardinal-Infante managed to assemble an army and almost miraculously repelled the much larger Dutch force, which lost several hundred men dead (one of whom was William of Nassau's only son), another 2,500 taken prisoner, and significant amounts of artillery and baggage.The Battle of Kallo was the largest action of the Spanish-Dutch War, as well as the only pitched battle and the worst Dutch defeat of the late Eighty Years' War.While no major offensive operation was carried out against the United Provinces by the Spanish Army of Flanders during 1636–37, in July 1637 the statholder Frederick Henry, Prince of Orange, marched into northern Barbant in command of an army of 18,000 soldiers and invested the Spanish-ruled city of Breda.