WWII 5/38 shell casing

I have acquired a 5"/38 shell casing, and would like to find out what some of the number and letters mean. The base identifies it as a 38 CAL. 5 IN MK 5, with a date of JUL 1945. The contractor was RMCO, but do not know what that is short for. After the RMCO appear 01 2431. There is a device in the center shapped like a Maltese Cross. Each of the four arms of the “cross” has one of the following: HW 172 MK. 131
45 13-1
It appears as if this “cross” was meant to be rotated as nescessary (I have not tried it)
In the center of the “cross” is a ring which appears to be made of nylon, and in the center of that is presumably where the firing pin hit the base of the shell. I have been given to understand that this was an Anti-Aircraft shell, but do not know for sure. All above information is stamped into the metal.

Additionally, there are some BLACK LETTERS and numbers which have been machine/hand stamped. They are: BI 939 McA.45 and 1018 NCIcIS. I am assuming that these were added after the shell was made by the Contractor. Would appreciate any information that the Forum can contribute. The “45” above appears below the “HW”, and the “13-1” appears bellow the “MK.”


You have a very typical 5"/38 powder case from the WW II period. 5"/38 means the gun bore was 5" in diameter and the barrel length was 5" x 38 = 190" long. The gun was dual purpose meaning it could be used for both anti-aircraft and for surface targets. 5"/38 guns were mounted on nearly every major US warship in WW II, and many other countries as well. It was also used on many smaller warships and auxilliaries, as well as on US Coast Guard vessels.

MK 5 is the designation for the case. The “maltese cross” shaped thing you see is the primer. It is a combination primer meaning it can be fired by percussion or by electric. The nylon ring is an insulator that seperates the primer from the rest of the case allowing an electric current to flow through it, igniting the priming mixture. It is shaped to allow a spanner to be used to screw the primer in (and out).

All of the numbers and letters that you see are information such as lot numbers, stock numbers, inspectors, etc, identifying the case. I doubt if you’ll find anyone here that can tell you what they all mean. I was a 5" Gunners Mate and most of them are Greek to me. RMCO is the manufacturer, one of many during WWI and I have no idea what it stands for.

I hope this helps.


I don’t know if it is the same as RMCO but here is my post about REMCO from many years ago viewtopic.php?f=1&t=1281&p=6293&hilit=RMCO#p6293

I don’t think REMCO has/had anything to do with Naval artillery ammunition during WWII and thus is not the same as RMCO. I don’t know the name of the latter, however. Out of my field completely.

Thank you, Ray, for your informative reply.

I was a crypy on carriers, and thus had no contact with anything larger than a .45. The information about the primer was particularlly interesting and I suspected that the device had to do with the firing. Hopefully, someone out there will come up with information about RMCO, and maybe some of the other information on the casing (like the purpose of the shell). I have contacted some folks at various USN sites, and they didn’t have a clue. Preasumably, I was talking to the wrong people- but it is difficult to know where to start. Were shells specifically designated for particular use (AA/Surface), or was that determination made just prior to firing?Seek and ye shall find… Thanks again.

The type of projectile would depend on the mission. The mount/gun captain would call the ready service room/magazine to request the proper ammunition. A peacetime exercise would be well choreographed. The ammunition to be expended would be located and marked prior to the shoot.

The wiki entry on the 5"/38 gun may help put the cartridge case and its use into perspective.


What Roundsworth said. The projectile was everything. I’d guess that 90% (or more) of the powder cases were full charge, what we called “universal”. They could be used for everything. There were also cases with reduced charges for special purposes such as Star Shells, clearing obstructions, and the like.

I’ve looked through my list of manufacturer codes and could not find a RMCO. But there were literally hundreds of manufacturers during WWII and most of them manufactured other items during peacetime. Once the war ended they went back to their old business. RMCO could have stood for Rogers Machinery Company of Podunk Michigan, who manufactured plows, for all I know.

I’m not sure if you’ll find anyone who can tell you what all the markings mean. As I said, they were lot numbers, stock numbers, powder numbers, inspector initials, arsenal/armory/depot codes, manufacturing dates, etc. Every time someone touched the case during its manufacture it was stamped. The information meant very little to sailor boy handling and firing them. Likewise with the projectiles. We went by the colors more than anything else. That told us everything we needed to know.


I have a MK 5 case made by RMCO in Nov 1944.


FWIW There are some WW2 British calibre cases we see here in the UK made by a company in Canada called “Robert Mitchell and Co.” These are stamped with the maker’s mark “RM/C”. The “/C” was used on cases made in Canada.

I am probably wrong here, but could there be a connection? Did the USN use any Canadian-made cases?

Found out today from an “unexploded ordnance technician” that RMCO on the base plate of my shell stands for “Remington Manufacturing Company of Philadelphia, PA”. The name is traditionally associated with the typewriter manufacturing industry, but in guess in wartime you retool to make what is needed for the war industry.

I don’t think that information is accurate- but do not know the right answer.

This case was made by Rheem Manufacturing Company at their plant in Birmingham, Alabama (former plant of American Radiator and Standard Sanitary Corp. purchased in 1942).

During WWII there was another US manufacturer using the “R.M.Co.” marking in Thompson magazine pouches and fabric belts (1916 Patent). This was the Russell Manufacturing Company of Middletown, Connecticut.

How sure are you about the Rheem connection? I’ve recently seen a post indicating origin of shell might have been Rogers Manufacturing Co., out of Podunk, MI.


I hope you have your tongue firmly planted in cheek, as I did when I mentioned the Podunk Plow Co possibility.

If Fede said it, I would bet my next meager Social Security check on it. Assuming it does not get sequestered.


For what it is worth, there REALLY is a Podunk, MI. It is about 30 miles from where I live. I have not been there for a few years, but as I remember it, there was NO industry there. It is just a small farming community.

Ray, thanks for trust me your social security check’s fate. I have no information about this “Rogers Machinery Comapny” as ever involved in anything barely related to ammunition. The Rheem Mfg Co was a huge company and by 1942 had 13 plants in the US and 2 in Australia, and also manufactured projectile shells, practice bombs, depth charge cases and ammunition containers. Their last “Ammunition Manufacturer” symbol assigned was “RMO” (1999).

I guess my little tounge-in-cheek comment got a little out of hand. I should have saved it for April 1st.

There is no Rogers Machinery Company as far as I know. That is a name that I made up to illustrate that RMCO could have stood for almost anything. There really is a Podunk MI and I used that for Ron’s benefit.

Sorry guys. I’ll be more careful from now on.


I have found more references of cartridge cases and shells made at different plants of Rheem Mfg Co:

  • Chicago, IL: bodies, bomb practice - 1941
  • Las Vegas, NV: 105 mm shells - 1945
  • Dallas, TX: Body, shell, 4.2 inch chemical mortar, M3 (also container) - 1945
  • San Pablo, CA: 81 mm mortar shells - 1952
  • San Pablo, CA: 155 mm shells - 1952
  • San Pablo, CA: 3"/50 Cal cases - 1952 (“in full production shortly”)
  • San Pablo, CA: 3"/50 Cal cases - 1953
  • San Pablo, CA: 5"/38 Cal cases - 1953
  • New Orleans, LA: 90 mm M19B1 steel cases - 1953
  • Burlington, NJ: 75 mm cases - 1955

Also found a picture of a 90 mm M19 brass case made by RMCo in 1945 which was loaded at the Ravenna Army Ammunition Plant (base and primer marked RVA).


Pshaw, I don’t squat about these things- I’m just trying to follow up any lead I get. There’s got to be an answer. Coincidentally, for some reason there are 3 Podunks in Michigan…