When he passed a one-year exam, he entered on 26 April 1868, as a midshipman in the North German Federal Navy.
From 1886 to 1888, he was commander of the gunboat SMS Wolf on the East Asian foreign station.
On 15 November 1888, he was promoted to corvette captain and in the same year commander of the torpedo department in Kiel.
In May 1896, Jaeschke was ordered back to Berlin to take over the Foreign Department in the German Imperial Naval High Command.
On 10 October 1898, Jaeschke was appointed by Alfred von Tirpitz as governor of the German-leased Kiautschou Bay concession, but only arrived at Tsingtau on 18 February 1899.