Passage: Kurfürst Friedrich Wilhelm served as the flagship of the Imperial fleet from her commissioning in 1894 until 1900. She saw limited active duty during her service career with the German fleet due to the relatively peaceful nature of the late 19th and early 20th centuries. As a result, her career focused on training exercises and goodwill visits to foreign ports. These training maneuvers were nevertheless very important to developing German naval tactical doctrine in the two decades before World War I, especially under the direction of Alfred von Tirpitz. She, along with her three sisters, saw only one major overseas deployment, to China in 1900–1901, during the Boxer Rebellion. The ship underwent a major modernization in 1904–1905.

Question: How many sisters did she have?
three