In the search for the optimum hybrid system for the premium motor car, the engineers were already sure of one thing right from the concept phase: a Mercedes-Benz SUV with a hybrid drive would have to share the same typical brand attributes as any other Mercedes vehicle. Essential elements such as the greatest possible active and passive safety, optimum ride comfort and ease of operation, uncompromising reliability over a long period and high-quality workmanship with select materials would have to be on a par with a comparable, conventionally powered standard-production vehicle. And all combined with the greatest possible efficiency. At the same time, the drive system should be testimony to the company's innovative strength and cutting-edge technology. These objectives demanded a complete development cycle – the kind of process any new model family developed from scratch would undergo. Until the Mercedes-Benz ML 450 HYBRID reached series-production maturity, the engineers and technicians clocked up a total of four million kilometres, taking in some of the world's most extreme climatic conditions to prove the system's reliability, be it in the sub-zero Arctic circle, the searing heat of arid desert regions or in the sweltering, humid temperatures of the tropics. The work was supplemented by an extensive test-rig programme and detailed simulations as part of the "Digital Prototype". An important aim during development was to optimally match the various subsystems within the powertrain. System matching enables the various drive modes to be easily used while the customer is driving.