Complex sentence: In 1943 an attempt was made to upgun the Churchill by using Heavy Churchill tanks modified to take a 17pdr gun similar to a Sherman Firefly, this resulted in the six Tank, Infantry, Black Prince (A43) in May 1945.
Split into simpler sentences: In 1943 an attempt was made to up-gun the Churchill by using Heavy Churchill tanks modified to take a 17 pounder gun, as was done with the Sherman Firefly. This resulted in the six Tank, Infantry, Black Prince (A43) in May 1945.