Commonly-used civil guidance and standards in the safety-critical software industry (IEC 61508, EN 50128, DO-178B) constrain development activity and generate process and product evidence. However, procurements for UK defence systems must be supported with a safety case assessed against Def Stan 00-56 Issue 4. This paper studies the use of evidence from civil guidance and standards in arguments towards DS 00-56. The approach is centred on a particular application, the KCG qualified code generator, and is based on a generic software contribution argumentation approach. The results show that issues arise in substantiating failure conditions, choosing a suitable level of detail in the argument and relating detailed explanations to the structure of the evidence. Explicit argumentation was found to be useful in addressing each of these issues.