About Centiradians
The centiradian, or centrad (crad), is one hundredth of a radian – the radian with the prefix centi- applied.
A full circle is 2π radians, which is about 628.3 centiradians.
In practice small angles are given in milliradians or arcminutes rather than centiradians. 1 centiradian is 10 milliradians, or about 34.4 arcminutes.
About US WW2 Milliradians
The US wartime mil was an artillery unit, a rounded milliradian, and a right angle came to exactly 1,000 of them (4,000 to a circle). A true milliradian is smaller: 6,283 fit in a circle.
In World War II American artillery crews set elevation and direction in mils, reading the angle between the target and the gun from an aiming circle.
There are 4,000 US WW2 milliradians in a full circle.