Born in the lower nobility, Del Águila joined the Tercio de Sicilia at 18 and participated in several operations under Álvaro de Bazán against the Ottoman Empire. In 1567, deploying in the Low Countries to join the quagmire of the Dutch Revolt under the command of Julián Romero, Del Águila would ironically have his first feat there in the disastrous Mutiny of Alost, where the tercio rose up by an endemic lack of payments (British pirates had part of the blame) at the same time as Waloons and Germans mercenaries switched sides and let the enemy in the base of Antwerp. Romero, Del Águila and other officers managed to re-direct the mutiny into miraculously capturing the city, but this was followed by the infamous Sack of Antwerp, where the still money-hungry imperial army proceeded to violently loot the place for days, causing a fire that accidentally destroyed 80 houses. Loots were commonplace at the time and this wasn't the worst case, but the destruction and its related scandal were a huge blow to the imperials' reputation and worsened the course of the war.
Del Águila spent the next years going to and coming from the Netherlanda, although he had better luck there, eventually forming part of the staff of the general Alexander Farnese and sharing his military exploits (his tercio got finally paid all what was required, if you are curious). His next great showing would be the more crowd-friendly Miracle of Empel, where a Dutch army of 30,000 artfully flooded the Spanish camp with dams and attacked them on boats, only for the the meager 6,000 defenders or so to destroy them, in a big part thanks to an incredibly timely freezing of the waters. After many victories against Dutch and English forces, Del Águila was called back with honors by Philip II to command his own tercio and follow the Spanish Armada to England, but as the invasion backfired horribly, he was sent instead to France in order to help against the Protestant King Henry IV. Juan's service record would reflect that the Spanish Empire was overextending grievously by opening so many fronts, but he again performed as one of their best men around.
After receiving a well-earned break in the action in 1595, and maybe still thinking in his original destiny, De Águila made an unexpected move and decided to organize his own little Spanish Armada, sending a flotilla with 400 arquebusiers under his right-hand man Carlos de Amésquita and guided by an English Catholic spy. The fleet hit Cornwall, routed its defenders and made due before Sir Francis Drake could catch them, making Amésquita the first Spaniard to take the fight to England ground in many years (thought not the first, being preceded by Fernando Sánchez de Tovar and Pero Niño). This success eventually rekindled Philip II's hopes that an invasion of England was possible after all, so he entrusted the Third Spanish Armada to Del Águila and Martín de Padilla in 1597. However, as with the two previous instances, the 178-ship fleet was trounced by an equally huge storm. This time, some ships actually managed to deploy troops in Falmouth, but as the rest of the fleet never arrived, they were forced to return home.
Del Águila and Padilla were discontent with Philip's way to organize armadas (read: bad), and this didn't improve when Juan was accused of embezzlement, although he managed to prove his innocence. As a rebound, he was given yet another armada, this time a small 33-ship issue directed to deploy in Ireland and help the local rebels against the English crown. Not without some storm on the way, Del Águila disembarked and snatched some early victories against the English army of Charles Blount, Baron Mountjoy, attracting the loyalty of local nobles, but a mix of uncoordination, difficulty to get reinforcements and the abandonment of several Irish contingents led the Spanish-Irish coalition to a defeat in Kinsale, forcing Del Águila to surrender and return home. This would be the end of Del Águila's tumultuous life, as he fell sick and died shortly after in midst of ungrateful recriminations for his performance. He received a posthumous court-martial, but not having his own testimony means we will never know if he could have got away with it.
