Defence is critically dependent on its own and national infrastructure for energy, water, information, transport, telecommunications and emergency services. The degree of interdependence between defence and national infrastructure varies across these basic services. This combination creates a very complex dynamic system. Review of Defence locations usually start with the logical system boundary the fence that surrounds the site. Infrastructure considerations which link and support the sites, these are viewed as external to Defence and as such beyond the Defence Organisational influence, missing the strong interdependency found "over the fence". This paper describes an approach to understand the dependencies and fragilities which impact defence resilience. This resilience approach identifies potential impacts on defence capability, points/areas of failure when data sets are combined from both internal and external sources. A number of themes emerged from the analysis including strategic shocks, chronic stressors (e.g. perpetually under-resourced areas), divergent views (e.g. alternative lines of command /priorities), vulnerabilities, graceful degradation (e.g. aging assets) and future plans. In order to achieve this, we extracted data from many Defence inputs such as: the industry policy statements, estate management, logistics supply chains and the Force Structure Review /force mix assumptions and scenarios. In addition, external data was accessed from sources such as Northern Territory government, Australian Bureau of Statistics, Attorney Generals Department /Critical Infrastructure Protection Modelling Agency, Engineers Australia, and Geoscience Australia. This dataset was used to cross reference the subject matter expert (SME) views collected at workshops and via surveys. This allowed SMEs to provide the impact the historical events that impacted Defence activities, and for those impacts to be categorised into themes, case studies and exemplars. This work demonstrates the impact of critical infrastructure on Defence capability, and highlights the importance of a resilient infrastructure. Actions that bring about change in a specific area often lead to unanticipated and potentially unwanted consequences elsewhere. Treating resilience as a component of the defence system recognises that our world is changing and that changes occur often in an interlinked way.