E-Series
German Entwicklung Series Tanks in late-WWII

The Entwicklung series (en "development"), or the E-Series, was a late-World War II attempt by Nazi Germany to produce a standardized series of tank designs. There were to be standard designs in six different weight classes (E-5, E-10, E-25, E-50, E-75, and E-100) from which several specialized variants were to be developed. This intended to reverse the trend of extremely complex tank designs that had resulted in poor production rates and mechanical unreliability.