Based on the ultimate goal of developing a 300 watt polymer electrolyte membrane (PEM) fuel cell system weighing <=5 kG for man-portable power supply and similar applications, the proposed Phase I project will be pursued with the limited objective to: (a) design and develop a prototype unit; (b) demonstrate the desired performance level and compliance to weight limit; and (c) understand the operational characteristics parameters and requirements of the unit. In order to achieve these objectives a 4-cell prototype fuel cell unit will be designed and assembled using; (i) laminar (planar) multi-cell configuration instead of conventional bipolar stack; (ii) lightweight hardware components, particularly unipolar plates developed using platelet technology; and (iii) H Power high performance electrode/MEA technology. The performance of the prototype unit will be critically evaluated to demonstrate practical feasibility of the proposed power unit. Operational characteristics/parameters will also be determined in order to assess the need of ancillary devices; e.g., for heat and water management in the fuel cell assembly.