The design staff continued to refine the new ship, and by September 1905, several variants had been proposed, including "F", which replaced the four single-gun turrets with an equal number of twin-gun turrets. The 17 cm guns were also replaced with twelve guns on the basis that they offered a much higher rate of fire. An improved underwater protection system was adopted as well, resulting in the design finalized as "G", which was approved on 4 October. Internal rearrangements to the magazines and boiler rooms resulted in "G2", while an attempt to move all of the gun turrets to the broadside was presented as "G3", but this proved to be unworkable. "G2" was chosen for continued refinement, becoming "G7" and then "G7b", which the Kaiser approved on 3 March 1906. The initial arrangement with three funnels was altered to just two, and a new bow was incorporated, securing approval from the Kaiser on 14 April as "G7d". Construction of the first vessel was authorized on 31 May; another member was added shortly thereafter, with another two authorized for the 1907 construction program.