A military unit cover designator (MUCD, MUCK-dee, Chinese: 部队代号; pinyin: bùduì dàihào) is a unique five-digit number used by the People's Liberation Army of the People's Republic of China to externally identify military units.
The unit's TUD is used by members of the regiment, in common discourse, and among defense analysts, while the MUCD is used on stationery letterheads, newspapers, banners, magazine articles, and signs at the entrance to military facilities.
[1] Some units, namely those conducting sensitive and secretive operations like those of the Third Department (Operations) of the Joint Staff Department, may only be known by their MUCD as their TUD has not been discovered.
[1][3] Begun shortly after the 1949 communist victory in the Chinese Civil War, MUCDs were originally four-digit numbers until 1975 when, as part of Deng Xiaoping's counter-Maoist military reforms, the five-digit system presently used was introduced.
[citation needed] MUCD's changed again in 2000 and once more in 2016 following the massive reorganization of the PLA under Xi Jinping that included the transition from military regions to theater commands, the Second Artillery Corps to the People's Liberation Army Rocket Force (PLARF), and the establishment of the Strategic Support Force (PLASSF) which incorporated various functional units of the General Staff Department (which became the Joint Staff Department).