Which type of projectile is used for obscuring visibility on the battlefield?

The correct answer is smoke rounds, as they are specifically designed to obscure visibility on the battlefield. Smoke rounds are employed to provide cover for troop movements, concealment of equipment, or to signal other units while creating a smoke screen that can hinder enemy observation and targeting. These projectiles deploy smoke upon detonation, which helps in preventing the enemy from seeing and accurately targeting friendly forces.

In contrast, high explosive rounds are meant to destroy targets and inflict damage rather than obscure visibility. Illumination rounds are used to light up an area at night or in low visibility conditions, helping forces see the battlefield more clearly. Fragmentation rounds are designed to injure or kill personnel and destroy equipment with shrapnel rather than serving any purpose related to obscuring vision. Therefore, smoke rounds distinctly serve the function of visibility obstruction on the battlefield, making them the most appropriate choice.