The recruitment of the Jäger volunteers from the Grand Duchy of Finland was clandestine and dominated by Germany-influenced circles, such as university students and the Finnish upper middle class. The recruitment was however in no way exclusive. In all, over 1,100 volunteers are estimated to have "slipped off" to train in Germany.
The recruits were transported across Finland's western border via Sweden to Germany, where they were formed into the Royal Prussian 27th Jäger Battalion. The Jäger Battalion fought in the ranks of the German Army from 1916 in the battles on the northern flank of the eastern front.
After the outbreak of the Civil War in Finland the Jägers were engaged on the "White" (non-communist) side in the war and formed the nucleus of the new Finnish Army. In Finland, these 2,000 volunteers were simply called The Jägers (Finnish pl. Jääkärit).
Their contribution to the White victory was crucial, not least through improving morale. Educated as elite troops they were also fit to assume command as officers over the untrained troops of the Civil War.
Immediately after the Civil War, they were given the right to use the word Jäger in their military ranks. Many of the Jägers continued their military careers. In the 1920s a long feud between officers with Jäger-background and Finnish officers who had served in the Russian Imperial army was concluded in favor of the Jägers: Most of the commanders of army corps, divisions, and regiments in the Winter War were Jägers. The Jäger March composed by Jean Sibelius for the words written by Jäger Heikki Nurmio, was the honorary march of many army detachments.