Maritime Transportation Systems (MTSs) are essential for world trade; it is crucial to understand how these systems may fail, to be able to maintain their capacity. In this paper, the MTS is seen as a throughput mechanism; a technical system which serves its purpose by moving goods for its dependents. Understanding which key functions and capabilities are prerequisite for the ability to move goods, the loss of which are the failure modes, allows for the creation of a 'business continuity plan' for the MTS. Through two surveys and interviews with maritime transportation industry stakeholders, it was observed that while stakeholders in the industry have a solid focus on frequent operational risks, there is a lack of awareness of vulnerabilities, as well as methods for addressing and planning for low-frequency high-impact disruption scenarios. The presented approach provides a structured set of matrices of the key functions of the MTS, allowing stakeholders to increase the system's resilience through preparing to restore this limited number of critical functions.