The Nassau class, which was composed of Nassau, Westfalen, Rheinland, and Posen, was the German response to the arrival of HMS Dreadnought, the first "all-big-gun" battleship, in 1906. The ships were unique in their main-armament configuration, which was hexagonal.[lower-alpha 2][47] They retained triple-expansion engines instead of more powerful turbine engines, and as a result, were slower than their British contemporaries.[48]