What is this part and is it necessary?

I think its something to hold the turret door in the open position and/or to stop it from swinging shut. If its on the full scale example, then it is necessary, in my opinion.

Matt:

Frank is, I am sure, correct - that little bit is the retainer that kept the hatch-cover from either slamming back onto a crew member or smacking into the view-port cover in front of the hatch. One appears on either side of the turret, and they do want to be there. They show up on pics of the real thing, although interestingly seldom in actual use! Looks like most crew who had those hatches open were sitting in the hatch and generally holding onto the cover, as versus having it all the way forward and latched (which wouldn't provide any cover or shelter for the crew member, and may not have looked "as military" in the eyes of either the crew or the photographers! (this latter just a snide quip given soldier's penchant for posing...!)

There is at least one very nice picture of a partially-built kit showing this piece in (probably) correct use! Go to the image at...

http://www.bpmodels.net/Model/PzIVC/Step29.JPG

One thing I would point out is that yes, there should / would have been a small peg on that piece which would be turned down to retain the hatch-cover forward.

Cheers!

Bob