Abbreviation help

[Explorer]

Don't know where to post this. Please move if necessary.

Can you help me out with this abbreviation. What does it refer to?

2./J.R.13 I

[naxos]

2. Kompanie of Infanterie-Regiment 13 - The ( I ) indicates the first Bataillon

[Explorer]

Thanks. Why does a J stand for an I as in Infantry?

[naxos]

Thanks. Why does a J stand for an I as in Infantry?

easier to read (distinction between Roman I for 1 and I for Infanterie)

[Explorer]

Interesting. But what about real J then?

[naxos]

Interesting. But what about real J then?

Is also abbreviated " J "