Complex sentence: The BCS included M13/40s, the most modern Italian medium tanks, which were were a vast improvement over the M11/39s used as part of the Maletti Group ("Raggruppamento Maletti").
Split into simpler sentences: The BCS included M13/40s the most modern Italian medium tanks. The M13s were a vast improvement over the M11/39s used as part of the Maletti Group ("Raggruppamento Maletti").