MIL-HDBK-1559, DEPARTMENT OF DEFENSE HANDBOOK: NUMBERS, SERIAL, AIRCRAFT GAS TURBINE ENGINE AND ENGINE MODULE ASSIGNMENT OF (14 FEB 1997) [SUPERSEDING MIL-STD-1559]. This standard describes the method of assignment and arrangement of letters and numerals used by the Military Services to identify complete engines and modules (major sub-assemblies thereof) as to the manufacturer and series in production.