This paper presents an integrated transient hydraulic model that describes the dynamic behavior of natural gas transport systems (GTS). The model includes sub models of the most important facilities comprising a GTS, such as pipelines, compressor stations, pressure reduction stations, underground gas storage facilities and LNG Terminals. The submodels are combined to an integrated network model and the algorithm for solving the resulting system of equations is detailed. The accuracy of the model is confirmed by benchmarking the model against results from the scientific literature and the commercial software SIMONE. Finally, the ability of the model to simulate the normal operation of a real world gas system and the operation in case of a supply disruption from a major entry point is demonstrated.