Which type of artillery round is used primarily for direct fire missions?

High Explosive (HE) rounds are designed to deliver a powerful blast effect, making them highly effective for direct fire missions. In these scenarios, the objective is to target enemy forces or fortifications with a high degree of accuracy and lethality. The HE round features an explosive filling that detonates upon impact, causing significant damage over a wide area, which is particularly valuable in combat situations where immediate enemy suppression is needed.

In contrast, smoke rounds are utilized for obscuring vision to facilitate movement or cover troop positions rather than for direct engagement. Illumination rounds are intended to provide light over an area during night operations or low visibility conditions, aiding in observation rather than destruction. Practice rounds are designed for training purposes, lacking the explosive components needed for combat effectiveness. Hence, the primary role of the HE round in direct fire missions positions it as the best answer in this context.