The linear meter scale is making me wonder how the thing works.
I agree, the scale was the first thing I noticed. Looks to be a DC movement. Could be the shunt doesn't belong to the meter.
I have GE antenna current meter, but they are direct reading meters, no external shunt needed and the scales are not linear.
You need to figure out what piece of military gear the meter was used in.
The needed info is not shown on the face of the meter, what's the full scale current of the meter. Normally, if there is no other ratings shown along the bottom of the face, you can assume it is a direct reading meter, whereas no shunt needed. But, like Dave points out, the linear scale doesn't seem correct.
Fred