M121 155 mm projectile
The M121/A1 155mm Projectile was a chemical artillery shell designed for use by the U.S. Army. It was designed to be used with approximately  of GB or VX nerve agents. History
The U.S. Army standardized the M121 shell in 1954 as an artillery shell capable of delivering sarin via a 155mm howitzer. Shortly after the discovery of VX in 1952, the U.S. Army Chemical Corps began experimenting with employment systems for the newly discovered nerve agent. The M121A1 was standardized in 1961 as a modified version of the original projectile with the additional capability of transporting VX as well as sarin. The M121 and M121A1 have never been used in combat and remaining stockpiles are currently being disposed of in accordance with the 1997 Chemical Weapons Convention. Design
The M121 was designed as a steel shell that was  long with the fuze assembly attached and  without the fuze. The center contains a burster, which is topped by a booster propellant, which subsequently screws into the fuze. the hollow portion of the shell is filled with  of sarin (GB). The M121A1 is identical to the M121 with the exception of it using a larger fuze assembly, which makes the entire projectile . The large fuze assembly allows for the M121A1 to safely carry and deliver  of VX or  of sarin away from the howitzer. See also
M104 155mm Projectile
M110 155mm Projectile
M687 155 mm Projectile

References

Chemical weapon delivery systems
155mm artillery shells
Chemical weapons of the United States