Huge pet peeve of mine, this militaristic way of thinking. Even police are civilians -- every one is, except for actual soldiers. Cops love to refer to everyone else as "civilians" but they're just hired security with extra perks.
A dictionary reflects current usage. It does not reflect correct usage.
Police in the US are not governed by the UCMJ and have no affirmative obligations in the way military do. They are also civilians under the Geneva convention.
A professional police force only goes back about 200 years.