When Japan opened the Pacific War with aerial attacks upon targets in the Hawaiian Islands, the Philippines and Malaya on 7 or 8 December 1941 (the date varied according to location East or West of the International Date Line) Australia was isolated from some sources of supply and had to create facilities for the production of weapons and ammunition.
Six small-arms ammunition factories were established and each was allocated a discrete two-letter code which was stamped on the base of the case of each round of ammunition produced.  The following codes are listed as an aid to the identification of ammunition produced during the 1939-1945 War at Australian Small Arms Ammunition Factories (SAAF).
MF - SAAF  No. 1: Footscray (Vic).
MG - SAAF  No. 2: Footscray (Vic).
MH - SAAF  No. 3: Hendon (SA).
MJ - SAAF  No. 4: Hendon (SA).
MQ - SAAF  No. 5: Rocklea (Qld).
MW - SAAF  No. 6: Welshpool (WA).
Note:  SAAF No. 2 remained in operation post-1945 and was then allocated the MF code used formerly by SAAF No.1.