Complex sentence: The small ammunition capacity of the vehicle--six rounds--was also a problem, necessitating the creation of special ammunition carriers out of Fiat L6/40 tanks, one accompanying each Semovente da 90/53 in the field.
Split into simpler sentences: The small ammunition capacity of the vehicle was also a problem; only six rounds could be carried. This necessitated the creation of special ammunition carriers out of Fiat L6/40 tanks, one accompanying each Semovente da 90/53 in the field.