"Preussischer Adler" was laid down in 1846 and was launched later that year. She entered service in 1847 as a post steamer, operating the route between Stettin and St. Petersburg. During the German revolutions of 1848–1849, the ship was requisitioned by the Prussian Navy for use after the outbreak of the First Schleswig War between the German Confederation and Denmark in March 1848. At the time, the Prussian Navy was effectively powerless to prevent the larger Danish Navy from blockading the German coast; merchant ship owners in various German ports pressured Prussia to arm "Preussischer Adler" and another post steamer, "Königin Elisabeth", but the postmaster general initially refused to turn the vessels over to the navy, since doing so would break international postal treaties. Continued pressure forced the postal service to transfer the vessels, and upon her requisitioning, her deck was reinforced to support the weight of the guns added. While under naval service, the ship carried the prefix "SMS". During this period, from August 1848 to August 1849, the ship was commanded by her civilian captain, Paul Barandon, and she retained her civilian crew. The ship got underway for the first time as an auxiliary warship in August 1848, steaming first from Stettin to Swinemünde; by this time, the Armistice of Malmö had been signed on 26 August, temporarily ending the conflict.