NCAR/RAP has been developing and operating mesoscale and cloud scale data assimilation and numerical prediction systems for a number of US Army R.D/T ranges. Besides these routine operations, the system are also applied to support a few other DoD missions of varying duration. A 4-D continuous data assimilation method is employed, by which a broad kinds of observations, measured at synoptic and asynoptic times, are fully assimilated into a continuely running MM5, and weighted according to the observation times and locations. A multi-nested grid approach is used to deal with the multi-scale interactions and to cover a full scope of mesoscale weather processes with limited computing resources.