A system for mounting armor to a structure such as a vehicle hull has a base for attachment to the structure, an adapter engaged with the base and with the armor for coupling the base to the armor, and a fastener, for example a pin or a bolt) for rigidly securing the adapter with the base. The system advantageously permits retrofitting of previously unarmored structures and/or permits replacement of damaged or obsolete armor. A kit for retrofitting a structure with armor has a base for attachment to the structure, an adapter for engagement with the base and with the armor for coupling the base to the armor, a fastener for rigidly engaging the adapter with the base, and instructions for mounting the armor on the structure using the base, the adapter and the fastener.