He was hit by shrapnel from a grenade.

他被一枚手榴弹的弹片击中了。

《柯林斯英汉双解大词典》

He was preparing to throw the grenade when he was tragically hit by enemy fire.

BBC: VC hero L/Cpl James Ashworth 'supremely courageous'

He hurls a grenade at the enemy, giving cover to a third Ranger who rushes to their aid.

WHITEHOUSE: Medal of Honor for Sergeant First Class Leroy Arthur Petry

As you can tell, Corporeal Dunham died from the wounds he suffered when the grenade exploded.

NPR: Marine Receives Posthumous Medal of Honor