CPV code 50842000 designates Repair and maintenance services of weapon systems in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
50842000 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 50840000 (Repair and maintenance services of weapons and weapon systems).