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 cassis crista 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 milwaukee mnm1-600 and analyzed.