The Entwicklung series (from German Entwicklung, "development"), more commonly known as the E-Series, was a late-World War II attempt by Nazi Germany to produce a standardised 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 specialised variants were to be developed. This intended to reverse the favor of extremely complex tank designs that had resulted in poor production rates and mechanical unreliability. The E-series designs were simpler, cheaper to produce and more efficient than their predecessors; however, their design offered only modest improvements in armour and firepower over the designs they were intended to replace, such as the Jagdpanzer 38(t), Panther Ausf. G or Tiger II; and would have represented the final standardization of German armoured vehicle design. Indeed, nearly all of the E-series vehicles — up through and including the E-75 — were intended to use what were essentially the Tiger II's eighty centimeter diameter, steel-rimmed road wheels for their suspension, meant to overlap each other (as on the later production Tiger E and Panther designs that also used them), abandoning the interleaved Schachtellaufwerk roadwheel system that first appeared on German military half-tracks in the early 1930s. Jagdpanzer E-10 Said to have been designed by the Klockner-Humboldt-Deutz Magirus AG firm in Ulm, the E-10 project (development name - "Hetzer") was developed as a replacement for the Jagdpanzer 38(t). The name Hetzer was never officially used for the 38(t). The designs based on this new chassis would all be in the 10 to 25 tonnes weight class, and using only four Tiger II-style but larger all-steel road wheels per side in an overlapping layout for its main "slack-track" suspension with no return rollers and a rear drive sprocket. Much simplified was the suspension, which was intended to be based on the concept of using conical-spring Belleville washers for the E-series AFVs as a whole. These were simply bolted on to the chassis and could be easily removed for repair or replacement. This suspension system was later used on the Swiss Panzer 61. A most interesting aspect was the ability to lower the hull by placing the pivot points of the suspension units higher in respect to the hull bottom; by not having torsion-bars occupying the entire hull planform in the lowermost interior areas of the hull, but via cranks driven by hydraulic actuators on the