20mm Oerlikon "TM" gun

I came across a datasheet on Oerlikon color markings of a 20mm round for the “TM” gun.

While one can only guess on the caliber which could be 20x128 I wonder what the gun would be.

I asked back to some very knowledgeable people but so far no solid answer has surfaced.

Anybody to ID the exact caliber and gun?


The closest I can get to it, from my forthcoming history of auto cannon and their ammunition:

Oerlikon Type 5TG (KAB): 20 x 128 ammunition.

The Type 5TG, later renamed the KAB, was developed in the late 1940s from the experimental 2TMG aircraft gun but seems to have been less successful than the slightly later 204GK described below.

Could the “2TMG” have been related to the “TM” gun? I don’t know, but would be interested in the answer!

Tony, thanks.

The 2TMG would be in 20x128 then?

I think the TM should not be this one as the color code sheet was in the 1980s. Or did they accidentally carry on the initial (first?) gun designation for the caliber?

Could the TM here be for Training Munition?.

No, it is the gun designation.

Is it a malformed TM Trademark?

The drawing certainly shows the shape of the 20 x 128 - the 20 x 139 is more slender. Of course, it might not be accurate…

There is a canon 251RK from Oerlikon in 20mm , 25mm , 30mm, a couple off different type’s
This is a revolver canon in caliber 20x128 thats the same ammo as the canon 5TG 204K

Attached you find two Spanish brochures
Maybe someone who knows Spanish can give clear ness


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Yes, but the designation is RK for revolver kanon. It’s the meaning of TM which needs solving.

the case on right is brass ?
first time that i see a brass case in this caliber

Tony, it appears to be but as similar tables I have seen over the decades sometimes are just made “like something along the line” I learned not to trust generalized drawings since the case shape given here would not be the core subject of the table allowing some “flaws”.
This is why I decided to ask here and of course for clarification of the “TM”.

Jess, no, following Oerlikon designations this is definately not the case here.

Harrie, great document as such! Though my Spanish is useless here.

The “TM” hs is very valuable in this regard! It shows that this is a very early designation of of the gun as the brass cases are the first to having been made before they went steel!
So my suspicion of the “TM” being an early designation/design is correct.
Then it is surprising how this designation sneaked into a 1980s document as by that time there were several other designations in use for the 20x128 caliber (and are today).

Tony, can you share any more info on what I presume is a new book in the works? I don’t want to hijack Alex’s thread, but this sounds exciting!

It’s based on my first book, Rapid Fire (which came out 19 years ago) and contains similar general information about the development and use of automatic cannon 20-57 mm, but with two major additions, consisting of comprehensive listings of every case-type of ammunition, and every automatic cannon, I could find data on. So the book will be several times the size of Rapid Fire.

It has only been possible to do this because of lots of help from others who specialise in particular areas, as well as much information posted on this and other forums.

The first draft of the text is complete, but I still need to trawl through all of the sources I have collected to ensure that I haven’t missed anything, plus provide illustrations. The ammo isn’t a problem as I possess examples of virtually every case type (including replicas), but photos of the guns and installations which are free of copyright are patchier!

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Tony, do you have a release date for this?

No, not yet. I have only just started discussing it with my publisher.

…remaining off topic…

What happened to your proposed book on Naval weapons?, there is very little easily accessible info out there, particularly on the ammunition. I’d buy one…;).

I think Norman Friedman has cornered the market in naval weapons; I have a lot of his books, and they are generally very good. He doesn’t say a lot about ammo, but frankly once the calibre increases beyond 57 mm, I’m outside my collecting and comfort zones.

I will, of course, be including a lot about naval guns and ammo up to 57 mm in the new cannon book.