These early M48 tanks suffered from engine, transmission, track, and suspension problems. The first production vehicles suffered from excessive oil consumption and engine failures after only 1,000 mi (1,600 km). The gasoline engine managed only 0.33 mpg US (0.14 km/L), limiting range to 75 miles (121 km). The M12/T41 rangefinder was too fragile and often broke. Army Field Forces (AFF) found these tanks to be unsuitable for combat use in Europe and was regulated to limited use by US Army CONUS units until numerous shortcomings were corrected. Furthermore, some 120 hulls were found to have insufficient hull armor protection. These were denoted as the M48C and relegated by the Continental Army Command (CONARC) for non-ballistic training use by the Armor School at Fort Knox to train crewmembers and maintenance personnel.