What is a 1d Vehicle scale weapon?

[Infojunky]

Ok if a 2d weapon is a light AutoCannon

Does that make a 1d weapon a Heavy Machine gun?

 

[MongooseMatt]

An HMG is personal scale (was originally a 1D vehicle weapon, but that proved too powerful). A low-tech/very light autocannon would fit in at 1D. There is an argument that is where the current Light Autocannon should fall.