The Prussian S 4's were German superheated express steam locomotives with the Prussian state railways, later grouped as DRG Class 13.5 in the Deutsche Reichsbahn. They were an evolutionary development of the Prussian S 3. The first locomotive was built in 1898 by Vulcan, Stettin as a modified S 3. She was the first superheated locomotive in the world. She was initially designated as Hannover 74 and towards the end as the S 4 Cassel 401. Two further trials locomotives appeared in 1899 and 1900 as Hannover 86 and Berlin 74 also classed as S 3's. They were later reclassified as S 4's Hannover 401 and Posen 401.