Went looking and found these, Otto Frank was an Artilleryman, His unit is not mentioned on the couple of sites on his service, but by noting  a couple of things we can pin down his unit I think. First, Frank was from Frankfurt Am Mainz right, his Pickelhaube Cover bears the Numeral 3, there no chance he was in the 3rd Field Artillery Regiment, Feldartillerie Regiment General-Feldzeugmeister (1. Brandenburgisches) Nr.3., this regiment was garrisoned in Brandenburg Prussia.

 

Then that leaves the 3rd Foot Artillery, Fußartillerie-Regiment „General-Feldzeugmeister“ (Brandenburgisches) Nr. 3, despite having "Brandenburg in it's title the 3rd Foot Artillery was garrisoned in Mainz, taking in conscripts and recruits from that general area, Mainz being a little to the South West of Frankfurt, plus the fact that Frank wears Brandedburg Cuffs indicated Foot Artillery as Field Artillery wore Swedish Cuffs. On the close up we see 3 on the cover better, plus the standard Shoulder Straps in 1914, this Foot Artillery Regiment just had it number on them. Will be posting a couple more later.

Here we see the Brandenburg Cuffs signifying Foot Artillery.

And as a Unteroffzier.

The full shot, here we see the Brandenburg Cuff of the Foot Artillery

So sad, a hero with the Iron Cross, then his family is sent to their deaths 20 plus years latter by the people he fought for. I didn't know he survived the war. Amazing.

Lets add this one here rather than start a new topic.

Arnold Bernstein, another Artillery Officer

https://en.wikipedia.org/wiki/Arnold_Bernstein