In this article, a model based on finite element–boundary element methods (FEM–BEM) coupling is developed for the magnetic field computation in thin magnetic shells submitted to external magnetic fields. The model is formulated in terms of the reduced magnetic vector potential. Surface fictitious currents are used for the FEM–BEM coupling. Only the active arts are discretized by using edge elements. The model is validated by comparing with analytical results for a magnetic hollow sphere in a homogeneous magnetic field. An application to the evaluation of ship magnetization is then considered.