This is a WWII War Department copy of TM 9-721 Heavy Tanks M6 and M6A1 , an Easy 1 Productions manual on compact disc.    This not one of the poor reproductions that are easily found on the Internet; all scans are in jpeg. form and at 400 dpi.  The CD contains the manual plus 90 photos of a M6.  As always, if this CD is ever updated with new material, you are entitled to the upgrade.  Follow Easy 1 Productions on Facebook.