Estonia co-operates with Latvia and Lithuania in several trilateral Baltic defence co-operation initiatives, including Baltic Battalion (BALTBAT), Baltic Naval Squadron (BALTRON), Baltic Air Surveillance Network (BALTNET) and joint military educational institutions such as the Baltic Defence College in Tartu. Future co-operation will include sharing of national infrastructures for training purposes and specialisation of training areas (BALTTRAIN) and collective formation of battalion-sized contingents for use in the NATO rapid-response force. In January 2011 the Baltic states were invited to join NORDEFCO, the defence framework of the Nordic countries.