Let's get this back on "track".
I know this isn't exactly rare, but it's still cool:
Panzerjäger Tiger Sd. Kfz. 184. AKA Elefant
The Germans wanted an anti-tank weapon with punch, so they threw an 88 onto the leftover failed Tiger I Porche hulls to get this beast.
It had a few glaring faults. Way too heavy for it's engine an final drive, and it also lack a small caliber, infantry defense machine gun. How in the hell could they leave that off?
https://en.wikipedia.org/wiki/Elefant