This paper describes the creation of a hardware-in-the-loop demonstrator for use in evaluating network architecture and control concepts for marine electrical systems, as well as specific items of equipment. The demonstrator allows a scaled hardware network to be connected to a simulation of a multi-megawatt marine diesel prime-mover, coupled via a synchronous generator. This allows “more-electric” marine scenarios to be investigated without large-scale hardware trials. The method of closing the loop between simulation and hardware is described, with particular reference to the control of the laboratory synchronous machine which represents the simulated prime-mover. The throttle control to the laboratory machine requires two nested “PIDA” proportional-integral-derivative-acceleration controllers, to achieve tight phase matching with the simulation. The limit on simulation fidelity is the speed with which field current can be slewed, which requires more powerful field drive hardware than was used during this paper.