Abstract: This paper describes the design and evaluation of a mobile computer system that has the potential to support the Australian Army's dismounted infantry command and control functions. Whilst commercial hand held computer systems have made significant improvements in hardware, it has been observed that current software has not been designed to cater specifically to Australian Army needs. The work described in this paper represents the first step in identifying user and system requirements for this application. A concept demonstrator of the hand held computer (based on the Apple Newton 2000) was prepared for use during a field exercise in February 1998. The objectives of the study were to identify requirements of the hand-held computer as well as to investigate the methodology for evaluation of such systems. User feedback from the 1998 study is discussed as well as the future directions for this work. This includes the transfer of knowledge to a Windows CE based computer and the planned use of this system in the investigation of human performance and computer interaction issues.