"The M110 is fitted with the M2A2 203-mm / L25 howitzer. This howitzer was developed from the British 8 inch howitzer, used during World War I. The M110 is fitted with load assisting system to reduce crew workload. It fires HE-FRAG and nuclear projectiles. Maximum range with the standard HE-FRAG projectile is 17 km. Maximum rate of fire is only one round per minute. Sustained rate of fire is one round every two minutes. The M110 carries only 2 rounds. Ammunition is carried by escorting armored personnel carrier."
Source: http://www.military-today.com/artillery/m110.htm