Abstract : Full scale tests of candidate water mist systems were conducted in a simulated machinery space on the ex-USS Shadwell. There were no obstructions in the space and the fire threats were both pan and spray fires of up to 10 MW. These tests demonstrated the potential ability of water mist to extinguish both shielded and unshielded Class B fires in full scale, relatively uncluttered machinery space applications. Of particular importance from the standpoint of minimization of damage is the rapid reduction in the temperature of the space almost immediately after mist system activation. These tests also demonstrate the differences in firefighting capabilities of the candidate systems tested. While these results are extremely encouraging, modifications to the systems will be needed to shorten the extinguishment times and minimize potential fire damage. These modifications will be included in the Phase II tests.