Unit Description on a 1910 P08

[ldepersia]

I have a 1910 P08 handed down to me by my Father. He took it from a surrendering German Officer toward the end of WWII. The grip has the following Unit Description: 13.T.S.1.54

Can anyone tell me what unit that is?

Also, it does not have a hold open latch and spring. I originally thought it was missing/lost but I have seen some references to the fact that some of the earlier models did not include the hold open latch - is that correct for a 1910 model?

Thanks.