This is the 10257th most frequent Russian word.
боем
The Russian word "боем" means "by battle" or "in battle."
Here, 'боем' is used in the instrumental case of 'бой' (battle) to indicate the means by which the action of conquering occurred.
Они овладели крепостью боем.
They conquered the fortress through battle.
In this context, 'боем' is the instrumental singular form of 'бой' (beat), referring to the manner or accompaniment of the start of the drills.
Учения начались с боем барабанов.
The drills began with the beating of drums.
In this sentence, 'боем' represents the effort or fight needed to address a challenge, metaphorically implying a struggle or direct effort.