The recruitement of the J?er volunteers from the Russian Grand Duchy of Finland had to be secret, and was dominated by the most Germany-influnced circles, such as university students and the upper middle class. The recruitement was however in no ways exclusive.
The recruits were transported across Finland's western border via Sweden to Germany, where the volunteers were formed into the Royal Prussian 27th J?er Battallion. The J?er Battallion participated 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 those of the J?ers were released, who intended to engage on the "White" (non-Socialist) side in the war. In Finland, these 2,000 volunteers were simply called The J?ers.
Their contribution to the White victory was crucial, not the least morally. Educated as elite troops they were also fit to assume command as officers over the untrained and uneducated troops of the Civil War.
Immediately after the Civil War, they were afforded the right to use the word J?er in their military ranks. Many of the J?ers continued their military careers. In the 1920s a long feud between officers with J?er-background and Finnish officers who had served in the Russian Tsarist army was concluded in favor of the J?ers: Most of the commanders of army corps, divisions and regiments in the Winter War were J?ers. The J?er March composed by Jean Sibelius to the words written by the J?er Heikki Nurmio, was the honorary march of many army detachments.