Abstract. In order to predict the immunity of a generic missile (GENEC), not only the electronic system but also the enclosure has to be taken into consideration. While a completely closed metallic missile enclosure shows a high electric shielding effectiveness, it is decreased substantially by apertures which could not be avoided by different reasons. The shielding effectiveness of the generic missile could be investigated by means of a hollow cylinder equipped with different apertures. Numerical simulations and measurements of this hollow cylinder will be carried out and analyzed.