The Thompson Sub machine gun
One of the most effective weapons in world war II, the Thompson sub machine gun was a staple for many of the United States' officers and tank crews over the course of World War II. While resistant to grit and dirt, the Thompson was fairly inaccurate and lacked a lot of power. As a Sergeant, Chapman would have likely carried this weapon during his landing.
M1 Garand
The Standard issue rifle for the ground troops of the US army, this was the most common rifle in the US' army during the war. It was accurate, powerful, and easy to disassemble. It's clip ejection system was unique at the time, as it automatically removed the clip after the last bullet was used.
The Bangalore
Primarily an explosive, this 'torpedo' proved to be extremely effective during the invasion. While bulky, it was very effective at clearing paths for troops as well as vehicles, it was able to remove barbed wire and other obstacles with ease. Its 3.85kg of TNT was very helpful in clearing paths, particularity barbed wire and tank obstacles, to the cliffs of Normandy.