What type of weapon is the chain gun?

The chain gun is primarily classified as a 30mm cannon. This type of weapon is known for its ability to fire at high rates of fire while also being capable of using a variety of ammunition types, including programmable rounds for precision targeting. The design of the chain gun allows it to be air-cooled and fed from a belt, which facilitates rapid firing and reliable operation in military applications.

While the chain gun shares characteristics with other firearm types mentioned in the options, it is distinctly recognized for its caliber and functionality as a cannon rather than a rifle or machine gun. The 20mm rifle option suggests a smaller caliber and different operational role, whereas the 7.62mm machine gun refers to a different class of machine weapons, typically utilized for infantry support rather than mounted systems. The 50mm grenade launcher is also not accurate since chain guns do not typically operate in the grenade-launching capacity. Thus, the classification of the chain gun as a 30mm cannon aligns with its purpose and design within military armaments.