The 71st Armored Field Artillery had (3) M4 tanks used for forward observation. They were M4 Sherman -Mid Production tanks, cast front - welded sides, with a Continental R975 C1; 9 cylinder, 4 cycle, radial gasoline engine and a 75mm cannon. Below are some good links for more on the M4.
Sherman Minutia Website http://the.shadock.free.fr/sherman_minutia/index.html
M4 Sherman Tank - The main American tank in World War 2 http://www.2worldwar2.com/sherman.htm
Medium Tank, M4 / M4 (Sherman) http://www.militaryfactory.com/armor/detail.asp?armor_id=40
M4 Sherman Tank http://www.strijdbewijs.nl/tanks/sherman/eng.htm
American Fighting Vehicle Database http://afvdb.50megs.com/usa/m4sherman.html
M4 Wikipedia http://en.wikipedia.org/wiki/M4_Sherman