The role of U.S. Army unmanned aircraft systems (UAS) is becoming increasingly important in tactical combat missions. Consequently, training critical skills required for manned-unmanned teaming (MUM-T) becomes more important, especially for UAS operators. In order to effectively train MUM-T skills, reliable and valid performance measures are required. Scaled observer-based performance measures can add objectivity to the process of assessing training outcomes, providing formative feedback, and tracking team progress. To this end, 36 performance measures were developed and evaluated to assess training-critical MUM-T skills. Draft performance measures were developed and refined with input from senior UAS operators and scout- attack pilots with MUM-T experience. For each performance measure, five-point behaviorally-anchored rating scales were produced representing “good,â€� “average,â€� and “poorâ€� performance of the skill. The content validity of the measures and the usability of the rating scales were determined by a second group of senior UAS operators and scout-attack pilots. Most MUM-T measures were deemed relevant to the mission and observable. Six measures with low consensus by participants on relevance and/or observability were determined not to be practically usable. Some of these unusable measures did not reflect the role of UAS aircrews in current MUM-T operations. The measures were designed to be collected as “over the shoulderâ€� observations. As such, a trainer, in the live or the virtual environment, could easily apply the measures. Because the resulting measures use quantitative scales that include exemplars of good-to-poor performance, they can be easily applied to unit performance assessment sessions, such as training â€� hot washâ€� and after action reviews.