Here's a little snippet from Wikipedia.. not my original source though.
Overall, Sturmgeschütz series assault guns proved very successful and served on all fronts as assault guns and tank destroyers. Although Tigers and Panthers have earned a greater notoriety, assault guns collectively destroyed more tanks. Because of their low silhouette, StuG IIIs were easy to camouflage and a difficult target. Sturmgeschütz crews were considered to be the elite of the artillery units. Sturmgeschütz units held a very impressive record of tank kills—some 20,000 enemy tanks by the spring of 1944.[2] As of April 10, 1945, there were 1,053 StuG IIIs and 277 StuH 42s in service. Approximately 9,500 StuG IIIs of various types were produced until March 1945 by Alkett and a small number by MIAG