The aim of this thesis is to design a computational method that can be used in modern stealth technology. In particular, the computational method should be capable to simulate scattering of ultra-wideband radar signals for military aircraft constructed with ferromagnetic radar absorbent materials. A full-wave boundary element method has been chosen because of its efficiency for electromagnetic scattering of electrically large structures. A time-domain method has been chosen because wideband signals can be simulated with a single run. Moreover, the future use of nonlinear constitutive equations for ferromagnetic materials requires simulation in time domain. To this end, the Time Domain Integral Equation (TDIE) method is used as computational method. More specifically, the numerical discretization of the Electric Field Integral Equation (EFIE) is given by the Marching-on-in-Time (MoT) scheme, which has been chosen because of its efficiency and accuracy. Instabilities prevent its industrial application to stealth technology, even for smallband and linear constitutive equations. In this thesis, a thorough numerical analysis on stability, accuracy, and robustness has been derived, resulting in clear guidelines for the choice of numerical parameters. Consequently, stable computer simulations have been achieved.