Original sentence: During the three month long Battle of Caen, over 400 British/Commonwealth tanks were lost before the British finally broke through.In November 1943 at Kubinka, during trials of guns proposed to be mounted on the IS-2, a 122-mm round fired from the A-19 gun passed clear through a captured Panther, penetrating both the front and rear armour.Instead, almost half the German tanks in Normandy were Panthers, whose frontal armour could not be penetrated by the 75 mm guns of the US Sherman tanks.Later in the war (1944 and on) Soviets found the quality of German armour dropped, lack of alloying metals made the plates too brittle.On the British side of the battles in France, the advantages of the Sherman Firefly were offset by the brute force frontal assault tactics of General Bernard Montgomery combined with a series of poorly coordinated air attacks on German positions.The area of Caen had the flat open terrain suited for tanks, and the Germans concentrated most of their tank forces there.This was due to then-current US armor doctrine which  assigned tanks to infantry support and exploitation roles, avoiding enemy tanks, and left the main anti-armor role to dedicated tank destroyers
Edited sentence: In November 1943 at Kubinka, during trials of guns proposed to be mounted on the IS-2, a 122-mm round fired from the A-19 gun passed clear through a captured Panther, penetrating both the front and rear armor.Instead, almost half the German tanks in Normandy were Panthers, whose frontal armor could not be penetrated by the 75 mm guns of the US Sherman tanks.Later in the war (1944 and on) Soviets found the quality of German armor dropped, lack of alloying metals made the plates too brittle.This was due to then-current US armor doctrine which assigned tanks to infantry support and exploitation roles, avoiding enemy tanks, and left the main anti-armor role to dedicated tank destroyers