The maritime transport system is one of the major means for transporting goods as safely, efficiently and environmentally friendly as possible. In this system, ports rep-resent hubs connecting maritime to other transport modes such as railway, road and aviation. Therefore ports and their services can be considered as critical bottlenecks where operations need to be sustained in a large variety of operating conditions. This chapter presents an analysis of the Vessel Traffic Service (VTS), a maritime shore-based information service which is part of a port’s infrastructure. VTS is a key service in guar-anteeing safe, fluent and efficient traffic flows in and out of a port, therefore making it a crucial part of a port’s ability to provide a constant service performance despite the large uncertainties that are inherent to maritime operations. Functional Resonance Analysis Method (FRAM) is used to build a functional model of the VTS to analyse the system design and its impact on the service supply chain’s ability to operate in a resilient manner, i.e. being able to sustain required operations prior, during and after disturbances or changes of operating conditions. While the chapter focuses on the mar-itime domain, it also provides an example on how a function-based approach can be used to understand and design service supply chains with a focus on how they achieve successful adaption to the large variety of operating conditions.