Things [in brackets]

I think you were right to start with. It's when the editor adds something that wasn't actually in the original quote to make the quote more understandable, or to explain something such as an obvious misspelling [sic].

In your example the speaker may have used a term that hasn't been explained, or the speaker may have used a sentence fragment when he was speaking. The speaker may have actually said, "F****** thing's within easy and rapid range . . ."

Others who actually work in the newspaper business might be able to give you a better and more complete answer.

When dealing with translations of fragmentary inscriptions, words are put in brackets to show that they have been inserted by the translator.

The same is true in spoken quotes. People don't always use complete sentences, or it's a brief selection from a longer dialog. In these cases, "[The missing pieces] are put in quotes so you know they did not exist in the original statement."

This is also the case in your example. The original quote might have been, "Baghdad is within easy and rapid range of perhaps 10,000 artillery tubes with a 57-second flight time." But the quoting author is already clearly speaking with Baghdad in context, and chose to alter the quote slightly.