This paper deals with the classification and analysis of failures of ultracapacitors to be used in rail launchers applications with the aim of investigating the influence of strong impulsive electromagnetic fields on their performance. Considering the very harsh environment present in rail launchers applications, a reliability analysis of components of the launch mass is very important to assess the failure modes and the relevant effects. To this purpose, we introduced a Failure Modes and Effects analysis methodology (FMEA) to ensure an optimal design and material choice as well as to evaluate the impact of all possible failure mechanisms and causes on the ultracapacitors. This approach allows to reduce or possibly eliminate the effects of potential failure modes before the launch mass design completion and before failures occur during the launch.