The Coriolis effect is the deflection of a projectile caused by the Earth's rotation. Typically a projectile will have to travel over 1000 yd (915 m) to observe the Coriolis effect. When using artillery and Naval guns, the Coriolis effect is observable. The accuracy of a shell is dependent on correct calculations of the Coriolis effect. With small arms the Coriolis effect tends to be minor while the spin drift plays a greater role.
The Coriolis effect is at its maximum at the North and South poles and negligible at the Earth's equator because of the angular velocity of the Earth's rotation. It tends to be important in arctic warfare scenarios as you are closer to the poles.
The Coriolis effect was conceived by the French scientist Gaspard-Gustave Coriolis in 1835.