The CSDP involves military or civilian missions being deployed to preserve peace, prevent conflict and strengthen international security in accordance with the principles of the United Nations Charter. Military missions are carried out by EU forces established with secondments from the member states' armed forces. The CSDP also entails collective self-defence amongst member states as well as a Permanent Structured Cooperation (PESCO) in which 25 of the 27 national armed forces pursue structural integration. The CSDP structure — headed by the Union's High Representative (HR/VP), Josep Borrell, and sometimes referred to as the European Defence Union (EDU) in relation to its prospective development as the EU's defence arm — comprises: