The work of the Data Safety Initiative Working Group (DSIWG) has been progressing since January 2013 with the aim of integrating the assessment of data safety into the system engineering development process, which incorporates system safety assessment. While the Data Safety Guidance is being continually improved and public emphasis on data in our lives is growing, Raytheon UK is integrating the data safety assessment into the system safety assessment process. Raytheon UK’s previous case study focussed on Air Traffic Management Systems (ATMS) but, since there are a multitude of safety assessment requirements which are customer-dependent within ATMS, this methodology paper focusses on defence and aims to develop sector-specific data safety guidance for defence engineering programmes in the UK.