In 1509, at the age of 18, Íñigo took up arms for Antonio Manrique de Lara, Duke of Nájera. His diplomacy and leadership qualities earned him the title "servant of the court", which made him very useful to the Duke. Under the Duke's leadership, Íñigo participated in many battles without injury. But at the Battle of Pamplona in 1521 he was gravely injured when a French-Navarrese expedition force stormed the fortress of Pamplona on May 20, 1521. A cannonball hit him in the legs, wounding his right leg and fracturing the left in multiple places. Íñigo was returned to his father's castle in Loyola, where, in an era that knew nothing of anesthetics, he underwent several surgical operations to repair his legs, having the bones set and then rebroken. In the end these operations left one leg shorter than the other: Íñigo would limp for the rest of his life, and his military career was over.