A commenter on an earlier thread, which touched on why police departments are seen as “paramilitary organizations,” writes:
Also relevant regarding the perceived more military nature of the police is the use now of the word “officer” to refer to what used to be called a “policeman” or “policewoman.” “Officer” is a term that has gained more currency in the last few decades as a result of gender equity (which also replaces “fireman” with “fire fighter”). I suspect you won’t see the phrase “police officer” much before 1960.
But why suspect when you can Google? Check out this Google Books query, and you’ll see that it had been used plenty of times before 1960. A similar query for “policeman” finds more, but not by a vast amount (365 to 137; ignore the reported hit counts, which aren’t reliable, even for comparison with each other, in Google Books, and instead go to the last page of the result).
Of course, it might well have been used even more frequently since then, compared to “policeman.” But it seems that both “police officer” and “policeman” were quite standard long before 1960.
Naturally, I can’t expect our readers to spend hours doing research before each comment. But an occasional quick query can do much, I think, to make comments and posts more accurate.