The Entwicklung series (from German Entwicklung, "development"), was a late-World War II attempt by Germany to produce a standardized series of tank designs. There were to be standard designs in five different weight classes (E-10, E-25, E-50, E-75 and E-100) from which several specialized variants were to be developed. The E-25 designs, in the 25-50 tonnes weight class, were to be the replacements of all Panzer III and Panzer IV based designs and was similar to the Hetzer tank destroyer.