Article 2 of the treaty covered joint development of defence plans; the mutual training of personnel in the use and defence against nuclear weapons; the sharing of intelligence and evaluation of enemy capabilities; the development of nuclear delivery systems and the research, development and design of military reactors. The treaty called for the exchange of "classified information concerning atomic weapons when, after consultation with the other Party, the communicating Party determines that the communication of such information is necessary to improve the recipient's atomic weapon design, development and fabrication capability". The US would communicate information about atomic weapons that were similar to UK atomic weapons. For the immediate future, that would exclude information about thermonuclear weapons. Confidential intelligence matters are also covered by the agreement. The UK government has not published those sections "because of the necessity for great confidentiality and because of the use that such information would be to other would-be nuclear states. In other words, it might well assist proliferation".