"The driver, who is the only member of the crew to be seated under armour, has a single-piece hatch cover in front of which are three M17 day periscopes. The middle M17 day periscope can be replaced by a passive night vision device. The Detroit Diesel Model 8V-71T engine is coupled to the Allison Transmission XTG-411-2A cross-drive transmission at the front of the hull.
Source: http://www.army-guide.com/eng/product1778.html