It's also used a lot in the field of external ballistics which is used not just by professional ballisticians and fire control operators, but by hundreds of millions of ordinary rifle shooters - especially competition shooters, but hunters to a lesser extent (albeit they are using the smaller milliradian).
Many scopes (rifle optics) have reticles which are divided by mils and the scope turrets often use 1/10 mil divisions (sometimes 1/20 mil for benchtest shooters). Also, the ballistic software (nowadays available as apps on phones) which most long range competition shooters use to calculate firing solution for drop and windage are typically set to milliradians to match the scope turrets.