The FAA has identified the Airport Surface Detection Equipment as a radar system that aids air traffic controllers in tow visibility conditions to detect surface radar targets and sequence aircraft movement on active runways. Though 35 major U.S. airports will have an ASDE-3 by the year 2000, its high cost precludes its use at hundreds of smaller airports; for them, low-cost COTS radar ('ASDE-X') shows promise as a controllers' aid in monitoring surface traffic and as a second sensor input to counteract shadowing, blanking and multipath problems. The FAA tasked the Volpe Center to evaluate Raytheon Marine's ASDE-X. The Phase I evaluation was made with Raytheon's Model ARPA M3450/18CPX-l9, a COTS radar with options added to adapt performance to the airport environment. This report details the characteristics, installation, and evaluation of this system at Milwaukee's General Mitchell International Airport (MKE). (Phase II will more closely approximate ASDE-3 functionality.) Test results show that, in low-visibility conditions, the system enhanced controllers' situational awareness, detected and displayed targets, aided movement area clearance, and enabled confirmation of pilots' reported positions and compliance with instructions. The ASDE-X's positive initial acceptance and tow cost ($100k versus ASDE-3's $6m) make it potentially a good choice for small airports seeking effective ground surveillance radar.