Whether you are a large multinational corporation or a small family owned business, all manufacturers, exporters, and brokers of defense articles, related technical data, and defense services (as defined on the United States Munitions List, Part 121 of the ITAR) are required to register with the Directorate of Defense Trade Controls (DDTC).
Don't forget, registering with DDTC does not automatically provide for export rights or privileges, but it is a precondition for the issuance of any license or other approval for export.