Abstract: This study investigates the effect of different levels of accumulated sleep loss on usability of an emulator of digital Command and Control (C2) technology. Three components of usability (efficiency, effectiveness and satisfaction) were explored. A sample of 13 military participants performed digital C2 tasks over four sessions. Sleep loss was induced by an additive combination of one night of sleep deprivation followed by two nights of sleep restricted to five hours. Neither effectiveness nor user satisfaction with the technology changed during accumulated sleep loss. When compared with baseline performance, there was a significant decrease in efficiency associated with accumulated sleep loss. There was also a slight recovery in efficiency after the second night of sleep restricted to five hours but levels did not return to baseline. Implications of these findings regarding use of the technology during military operations are discussed.