The objectives of this study were to design, develop, demonstrate and deploy a highly efficient drive-by-wire direct-wheel-drive transmissionless (differential-less and axle-less) propulsion diesel-electric drive systems for light, medium, and heavy hybrid electric vehicles (HEVs). The problems solved are extremely challenging because a number of long-standing problems in nonlinear analysis and control, optimization and design, manufacturing and technology developments, as well as technology transfer must be solved in order to design high-performance diesel-electric powertrains to be deployed in new generation of cars, pickups, trucks, busses and other vehicles. The major emphasis were placed to improve fuel economy and reduce emission, attain superior performance (vehicle and maneuverability, driveability and controllability), increase reliability and ruggedness, decrease cost and maintenance, etc.Innovative fundamental and technological developments were promoted through multi-organization industry-academia teaming arrangement. The results of test and evaluation of advanced components of diesel-electric drivetrains (high-performance turbocharged diesel, synchronous generator/starter, power converter, and traction motor/generator) are discussed. An advanced power converter with high-switching frequency IGBTs was used to control brushless traction motors. Thorough analysis was performed in the full voltage-current and torque-speed operating envelopes for generators and motors. The result of new design and test a prototype of an optimal energy-management system for diesel-electric drivetrains using advanced DSPs and microprocessors are documented. Novel control algorithms and innovative methods in design of optimal energy management systems are presented. These optimal energy management systems are needed to attain motion control and decision making with diagnostics. The decision making and control algorithms were integrated in the optimal energy management system to control a diesel-electric drivetrain. The high-level simulation architecture using MATLAB and SIMULINK was developed to perform comprehensive analysis. The analysis of the basic components of diesel-electric drivetrains was performed. The results of evaluations of diesel-electric drive subsystems (diesel-starter/generator-power converter-traction motor) on test-beds and nonlinear analysis of a hybrid-electric vehicle with an optimal energy management system are presented. In addition, the future development road maps and recommendations are reported in this paper.