Trịnh Tráng launched many major offensives against the Nguyễn, but all of them failed. The first attack lasted four months in the summer of 1627. The next was a sea assault, it was defeated in 1633. Two more assaults were made against the Nguyễn's mighty defensive wall in 1642 and 1643. This time, with the aid of advanced Dutch cannons, one wall was breached but the other wall held firm. 1643 also marked the resignation of the king, Lê Than Tông, in favor of his son, Lê Chan Tông. In 1648 a major offensive came to grief as the Royal (Trịnh) army was defeated at the battle of Truong Duc. The young king died at this time (Some people believe it was as a result of the battle) and so his father, Lê Than Tông, took the throne for a second time.