 Posen was ordered under the provisional name Ersatz Baden, as a replacement for the Baden, one of the elderly Sachsen-class ironclads. She was laid down on 11 June 1907 at the Germaniawerft shipyard in Kiel. As with her sister Nassau, construction proceeded under absolute secrecy; detachments of soldiers guarded the shipyard and also guarded contractors that supplied building materials, such as Krupp. The ship was launched a year and a half later, on 12 December 1908. Wilhelm August Hans von Waldow-Reitzenstein gave a speech at her launching, and Posen was christened by Johanna von Radolin, the wife of Hugo Fürst von Radolin, a German diplomat who hailed from the ship's namesake province. Initial trials were conducted through April 1910, followed by final fitting-out in May. The ship was commissioned into the fleet on 31 May. Sea trials were conducted afterward and completed by 27 August. In total, her construction cost the German government 36,920,000 marks.
