Complex sentence: An improved prototype, the T26, was produced as the M26 Pershing; the Army ordered and fielded 250 Pershings, but they arrived in Europe too late to have an effect on the conduct of the war.
Split into simpler sentences: An improved prototype, the T26, was produced as the M26 Pershing, and the Army ordered 250 Pershings. The Pershings were fielded, but arrived in Europe too late to have an effect on the conduct of the war.