Hi Bradley,
Yep, it's the 3rd variant of the Merkava Israeli Tank.
Revolutionary design (front engine, back door and capacity to accomodate infantary soldiers at the expense of paletized gun rounds)
It was a program initiated by Israel after the 68 and 73 wars when the suppliers of Israel let them down.
Being the kings of adaptation and ingenuity, they created the ball and chain armor. It is intended to detonate RPG's before they hit the turret base (apparently the most vulnerable part of the tank). It has proven effective against Sagger missiles too.
From what I could find the front .50 is now operated remotely, but it used to be operated by a guy lying over the turret (??).
The turret also has a mortar that can be fired from the inside witout exposing the crew.