In modern surface warship concept development it would be inconceivable to engineer the concept without safety in mind however, to assess the level of safety provided, it is often necessary to mature the design to a fairly advanced stage. Should the level of safety be found to be lacking, any resulting design changes are likely to be extremely disruptive and expensive. This is, in part, why Class Rules exist: to avoid the most fundamental safety concerns of basic designs. If we then shift focus from surface vessel design to submarines, where the design complexity is an order of magnitude higher and safety requirements are paramount, the impact of a design not meeting safety objectives could be prohibitive and the challenges of operating safely underwater in a three-dimensional domain would mean most surface vessel Class Rules are inappropriate with few submarine-specific notations available. As a result, the customer and designer alike have a vested interest in ensuring the design is working towards, and following, the right safety objectives from as early a stage as possible. To date early concept design safety assessment has largely been attempted by utilising Fault Tree/Reliability Block Diagram analysis to provide a quantitative assessment of safety. This method is entirely reliant on the accuracy of the core reliability data, using either known part data (thereby limiting innovation) or generalised data from sources such as the Non-electronic Parts Reliability Data (NPRD) where context is lost. The Naval Submarine Code (NSubC or NATO document ANEP-102) has been developed by the International Naval Safety Association (INSA) to provide a goal-based framework that enables naval submarines to be certified within a navy?s safety management system as safe to operate. Effectively providing a high-level safety element of Class Rules. This paper will discuss an approach, developed by BMT, to employ the NSubC as a base to evaluate concept design engineering safety and put it into the context of key safety events. This has established a process that allows continuous evaluation that matches the expected design maturity and can mature with it.