This paper addresses the need for predicting performance in a system of systems (SoS) during development. Historically, technical performance measures (TPMs) along with modelling and simulation have been used by senior decision makers to predict if a system under development will meet the required performance needs. This methodology does not appear to be directly translatable to SoS's for several reasons including the inherent complexity of the SoS and the operational flexibility the end user has in employing the SoS. An approach to dealing with the SoS performance prediction need is presented that addresses the use and integration of multiple technologies into a SoS and the decision maker's options in the use of these technologies. This approach is used to develop a metric defined as a 'SoS performance measure (SPM)', an equivalent to a TPM for a SoS. An anti-submarine warfare mission construct is used to demonstrate this new metric.