The Northern Jaegars were formed in 1179 from remnants of the military of the collapsed Principality of North Ambria, following the widespread poverty and devastation caused by the effects of the Salt Pale. Colonel Valestein, a figurehead in the country's military formed the Northern Jaegars as a means of supporting his country's population. The Northern Jaegars began hiring themselves out as mercenaries in order to secure foreign capital with which to help reconstruct their country. This would involve fighting in other nation's conflicts and proxy wars.
Given their ex-military origins, their equipment and level of training is noted to be quite high, even given the elevated standards of the jaeger corps. They operate out of and recruit exclusively from North Ambria and had no trouble finding new recruits whenever needed. There was even a Juvenile jaegar squad for under-aged individuals aspiring to join the main corps when they came of age.
Sometime prior to the events of the series, a young Sara Valestein was promoted from the juvenile squad into the ranks of the main corps. Her battalion had been hired to fight in a proxy war in remote Erebonia between a squabbling corporation and a competing noble family. Their opponents were another jaegar corp Nidhoggr but the Northen Jaegers soon had a decisive advantage. However, their unwillingness to harm civilians gave their opponents the opportunity to encircle Sara's unit and pin them down, placing them in a dire situation. Colonel Valestein broke through the encirclement with a relieving force and managed to rescue his adoptive daughter, at the cost of his own life. His departing words about his end being the ultimate fate of all jaegars gave Sara the resolve to leave that path. The remaining corps returned to their home country victorious and with a huge sum of Mira; none of their populace had to starve that winter and they were hailed as heroes. The sacrifice of their founder left a lasting impression on the corps.
During the November of 1203, the Northern Jaegers were hired as security guards for the Conrad Company's masquerade ball aboard the Lusitania. They were outmatched by Kevin Graham who infiltrated the party to retrieve an artifact along with apprehending its holder, Conard.
On November 30th S.1204, they raided Ymir under Duke Albarea's personal orders upon his discovery that Princess Alfin Reise Arnor was taking refuge there. Teo Schwarzer was able to take down most of them, but eventually they gained the advantage by taking a child hostage. They were then promptly defeated by an enraged Rean, before Vita Clotilde used a spell to coerce the jaegers to leave the village.
During December 24-25 S.1204, when Helmut ordered the entire province to obey his command, Celdic refused. In retaliation, Helmut sent his army and the Northern Jaegers to raze the village to the ground. Most homes were destroyed with major casualties as a result. The perpetrators were stationed at Aurochs Fort, but were defeated by Class VII with the remnants taken down by their former comrade, Sara. Shaken but admired by her resolve, the Northern Jaegers marched away with their objective completed thereby terminating their contract.
Following the annexation of North Ambria into the Erebonian Empire, the Northern Jaegers were seemingly disbanded and integrated into the the forces of the Imperial Army of Erebonia. A large group refused to accept this outcome and alleged insult to their pride, forming a new version of the corps. They collaborated with the seventh Anguis of Ouroboros, Arianrhod, in their efforts to 'retake the Phantasmal Blaze Plan', searching for a suitable battlefield to die upon with pride. They obtained new armour and equipment, and used the crest of the former North Ambrian country as their insignia to avoid misunderstandings.
In the Lamare Province, the new Northern Jaegers entered into conflict with an Erebonian hired force of Nidhoggr jaegars, eventually succeeding in 'winning the contract.' They then participated in a joint attack on Juno Naval Fortress alongside the Stahlritter and the Aion Type-α II. With most of the garrison out reclaiming the Railway Cannons, overcoming the paltry resistance of Marquis Ballad's personal guard was relatively simple. New and old Class VII breach the fortress and defeat the jaegars with the help of Sara, who prevents them from committing suicide while mentioning the legacy of the corps founder, and her adoptive father, Colonel Valestein. After coming around and seeing reason, the jaegers fall unconscious.
In Sara's bonding events, the Northern Jaegers and Nidhoggr eventually come to terms with each over and attend a memorial service for Colonel Valestein. They were then commissioned by the Imperial government, but terminate the contract and assist Class VII and the branch campus in repelling Gilbert Stein's 6th Enhanced Jaeger Regiment, who were besieging Eryn.