20x110RB Oerlikon with US Navy Property mark

I recently acquired this 20mm Oerlikon with a US Navy property mark. Fired US made 20mm Oerlikon and Hispano cases are common here, but this is the first I have seen with a property mark such as this.

Does anyone know if there was any reason why some were made without it?

Thanks for any info.

I have no answers, but it is a cool headstamp, and I’ll be looking for one. Maybe Liviu will notice this post eventually.


I haven’t found an answer, yet. I looked at a special publication by the old Texas Cartridge Collectors Org. entitled 20 x 110mm Oerlikon AA (no date), information compiled from Bill Woodin, Robert Leiendecker and Robert Eddy with drawings by Robert Mellichamp. In the section on US 20mm Oelikon ammunition they show over 25 different headstamps of which 10 show the US and anchor, with dates of 1942, 1943 and 1944 and various makers. Lots of other info but no explanation of why some cases have the mark and some cases do not have the mark. Something is bound to turn up eventually.


Maybe it indicates the ammo was manufactured to some particular standard established by the Navy. Similar to the Cal .30 AN ammunition (which wasn’t marked in any way other than the box label).

Just guessin’.


As far as I understood, the anchor with the 2 capital letters is an inspection mark. The capital letters represent the intitials of the ammo inspector. So maybe in this case the anchor with US doesn’t mean US Navy, but is the ammo inspector whose names begin with a U and an S. Maybe…

Another thought, is that the US navy only started using this caliber in 1942. I have heard that the first few batches of the US Navy order were to have the US Navy mark on so it didn’t get used or “re deployed” to other areas or countries, but with war time production being ridiculous and fast paced, this practice was dropped. Just another thought from a story.