MIL-STD-1394 and MIL-STD-1394B are Defense Standards, assigned as "PROVISIONS FOR EVALUATING QUALITY OF CAP CROWNS" by the United States Department of Defense, which control and maintain the specification. Like most mil-specs, they are freely obtainable at government websites. The cap crown is a part of the Combination cap.
MIL-STD-1394 and MIL-STD-1394B are often confused as being variants of IEEE 1394b, otherwise known as FireWire.
References
MIL-STD-1394 Wikipedia(Text) CC BY-SA