MIL-PRF-21260E, PERFORMANCE SPECIFICATION, LUBRICATING OIL, INTERNAL COMBUSTION ENGINE, PRESERVATIVE BREAK-IN (31 JUL 1998) [SUPERSEDING MIL-L-21260D]., This performance specification covers engine oils suitable for preservation, break-in, and lubrication of reciprocating internal combustion engines of both spark-ignition and compression-ignition types, and of power transmission fluid applications in equipment used in combat/tactical service (see 6.1, 6.7 and 6.9).