This is probably self-explanatory, but just want to make sure I've got it right.

Vessery's card says: "When attacking, immediately after you roll attack dice, you may acquire a target lock on the defender if it already has a red target lock token."

So if one of my other Empire ships has a target lock on, say, an X-Wing ... and Vessery attacks that same X-Wing ... it sounds as if he can roll his attack and then "immediately" slap a target lock icon on it ... and either maintain that lock into the next round OR spend the lock and re-roll the dice he doesn't like — as in right now, on this attack.

That's how this one plays out, yes?

Sort of a free Target Lock action as long as you're targeting a ship one of your other ships is already Target-Locked with?

If so, I can see this being pretty snazzy — assign a target lock from one of your ships at Range 3, while Vessery flies into Range 1, takes a Focus, AND gets the benefit of a free Target Lock.

That is exactly correct, yes.

Note also that it's "when attacking", as in any time you attack during your turn. This is only really relevant for Vessery with Cluster Missles; if the target is already target locked by someone else, after he spends his own lock to use the misssles, he gets to 1) roll attack dice for the first attack, gaining a lock 2) spend that lock if he chooses to 3) after the first attack is resolved, start a second attack, and roll dice 4) immediately gains a lock again, which he can then spend during this new attack.

Excellent. And I hadn't even thought of the ramifications of this on a Cluster Missile attack. That's really awesome.