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DaveyJ576 · 04-29-09, 05:53 PM

Luke,

The classification system of Navy enlisted ratings (job descriptions) is a constantly changing work in progress, and has been since they were first instituted in 1885. Some of the biggest changes came during the massive expansion the Navy went through in the WWII years. Ratings were established and disestablished, their descriptions and responsibilities changed, and the abbreviations and symbols were altered to fit.

In general, a Machinist Mate (MM) would have been responsible for the operation and upkeep of auxiliary systems such as hydraulics, air, fresh water, A/C, and refrigeration. Motor Machinist Mates (MoMM) would have been operators and maintainers of diesel engines and their associated fuel oil and lube oil systems. Prior to 1942 relatively few Navy ships were powered by diesels; we had mostly a steam navy and MM's would have covered both auxiliary systems and propulsion (along with Watertenders and Boilermen). The huge expansion of the fleet combined with the maturation of diesel technology resulted in a massive increase in the use of diesels and thus created a need for a specialized diesel operator/mechanic. Motor Macs were split off from MM's in 1942. Submarines, almost being a whole different navy itself, sometimes did things differently.

I perused the sailing lists of two boats (Tang and Barb) and found no mention of MM's being onboard at all during the war. A 3rd boat (Wahoo) listed several, along with MoMM's. Probably what you are seeing here is the earlier boat (Wahoo) still retaining her MM's from the pre-war organization, and the later boats (Tang and Barb) not having any MM's due to the split with MoMM's in '42. It was probably simpler for the smaller crew of a submarine to have only one rate doing both jobs, with MM becoming mostly a surface ship rate. This is not an unusual situation for submarines and this practice continues to this day. In 1948, the name of Motor Machinist Mate was changed to Engineman (EN) and MM's returned to submarines to operate and maintain the auxiliary systems.

When you have some time, surf over to these links:

http://www.history.navy.mil/faqs/faq78-4.htm

and

http://www.valoratsea.com/rate.htm

The info on the second link is not complete and has a few minor errors, but is still pretty good. Both sites should go a long way towards explaining the Navy's rather arcane enlisted rating system. I can also highly recommend the book Complete Guide to United States Navy Medals, Badges, and Insignia: World War II to Present by James G. Thompson (ISBN 1-884452-53-1). There is a little bit of missing information, but it is still pretty reliable.

04-29-09, 05:53 PM	#195
DaveyJ576 Officer Join Date: Nov 2008 Location: Norfolk, VA Posts: 241 Downloads: 30 Uploads: 0	Luke, The classification system of Navy enlisted ratings (job descriptions) is a constantly changing work in progress, and has been since they were first instituted in 1885. Some of the biggest changes came during the massive expansion the Navy went through in the WWII years. Ratings were established and disestablished, their descriptions and responsibilities changed, and the abbreviations and symbols were altered to fit. In general, a Machinist Mate (MM) would have been responsible for the operation and upkeep of auxiliary systems such as hydraulics, air, fresh water, A/C, and refrigeration. Motor Machinist Mates (MoMM) would have been operators and maintainers of diesel engines and their associated fuel oil and lube oil systems. Prior to 1942 relatively few Navy ships were powered by diesels; we had mostly a steam navy and MM's would have covered both auxiliary systems and propulsion (along with Watertenders and Boilermen). The huge expansion of the fleet combined with the maturation of diesel technology resulted in a massive increase in the use of diesels and thus created a need for a specialized diesel operator/mechanic. Motor Macs were split off from MM's in 1942. Submarines, almost being a whole different navy itself, sometimes did things differently. I perused the sailing lists of two boats (Tang and Barb) and found no mention of MM's being onboard at all during the war. A 3rd boat (Wahoo) listed several, along with MoMM's. Probably what you are seeing here is the earlier boat (Wahoo) still retaining her MM's from the pre-war organization, and the later boats (Tang and Barb) not having any MM's due to the split with MoMM's in '42. It was probably simpler for the smaller crew of a submarine to have only one rate doing both jobs, with MM becoming mostly a surface ship rate. This is not an unusual situation for submarines and this practice continues to this day. In 1948, the name of Motor Machinist Mate was changed to Engineman (EN) and MM's returned to submarines to operate and maintain the auxiliary systems. When you have some time, surf over to these links: http://www.history.navy.mil/faqs/faq78-4.htm and http://www.valoratsea.com/rate.htm The info on the second link is not complete and has a few minor errors, but is still pretty good. Both sites should go a long way towards explaining the Navy's rather arcane enlisted rating system. I can also highly recommend the book Complete Guide to United States Navy Medals, Badges, and Insignia: World War II to Present by James G. Thompson (ISBN 1-884452-53-1). There is a little bit of missing information, but it is still pretty reliable.