 Of the three ships in its class , only Derfflinger was ordered as an addition to the fleet , under the provisional name " K " . The other two ships were to intended to replace obsolete vessels ; Lützow was ordered as Ersatz Kaiserin Augusta for the elderly protected cruiser Kaiserin Augusta and the contract for Hindenburg was issued under the provisional name Ersatz Hertha , to replace the protected cruiser Hertha . 
