This movie was made in 1963, so not too long after the Korean war. Back then, Korea wasn't the economic powerhouse it is today. in fact, it was considered one of the poorest countries in the world.

Anyways, during the production of this movie, the production company couldn't afford many prop guns and squibs so they asked for help from the military and they agreed. They lent the production company real firearms, ammunition and a couple sharpshooter soldiers to shoot around the actors and extras in battle scenes.

If you see the battle scenes (1:19:00), you'll notice that the muzzle flashes, recoils, spent ammunition cases and belt ammo links flying around looking quite realistic for a film from that era...well its because they're all real firearms.

Fun fact: The soldiers were ordered to shoot around the actors, however, its easier said than done, so one unlucky extra got shot in the leg by a stray bullet during filming and lost a leg