The M110 155mm Projectile is an artillery shell used by the U.S. Army and U.S. Marine Corps. The M110 was originally designed as a chemical artillery round to deliver blister agents via howitzer as a replacement for the World War I-era 75mm chemical projectiles. The design was later repurposed as a white phosphorus smoke round for marking, signaling, and screening purposes. The white phosphorus variants of the shell also have a secondary, incendiary effect.