The Oseberg jacket was installed at the Oseberg field in the North Sea during the summer of 1987 and the production started on December 1, 1988. On March 6, 1988, a submarine accidentally impacted with the Oseberg jacket. This paper presents results from the evaluation of the importance of the damage to the overall structural safety. A nonlinear progressive collapse analysis is applied for the safety check. The theoretical computations are verified through evaluation of strain and acceleration time series recorded during the submarine impact. The reduction in the overall structural capacity of the jacket was in the order of 10 percent. However, the local member capacity was significantly reduced and it was necessary to remove the damaged member in order to obtain the initial level of safety.