Borgelin attended and successfully ended his education at the Royal Danish Military Academy in 1909. In 1919, when Borgelin was officer of the reserve and in charge of the Second Regiment Corporal School at the Værløse Camp in northern Zealand, he was given the offer of becoming company commander of a combat unit consisting of 200 men. In the spring of 1919, Borgelin and his "Compagnie Borgelin" arrived in Estonia with 12 Danish officers, 12 Danish junior officers and 189 Danish privates. The company participated in the Estonian and Latvian War of Independence under Estonian army command until 1 September 1919, when the contract expired and the company was disbanded.