French and English were used side by side for quite some time with the aristocracy primarily speaking French, and the commoner speaking English. Since you will rarely find a commoner speaking of weapons and combat in such detail, most words were just borrowed from the French that the military would have used. This is seen all over the place in the English language; you'll find more French the higher caste the term is used in.
Though, then there's the food thing. If you eat it, it's French (pork, beef, poultry), if you raise it, it's English (pig, bovine, chicken). I never quite learned why this is. Maybe it became distasteful among the elite to refer to their food as animals so they borrowed French again.