10/4/21:
Body armor was sometimes hinted at in the show (and actually seen in some of the TOS movies), but I don't think we've actually seen it in use. One of the early ideas for phasers is that they would also extend a personal shield to the user. This obviously was never done, but I could see body armor providing that to a limited degree.

Transcript
Panel 1
Tajaran Engineer: This is a waste of time.
    An "imbalance" in the ship, Glugtor says? The only imbalance is in his brain.
Tajaran Technician: Hoo hoo hoo.
Both Tajarans: ...
Engineer: Um... Was this hole always here?
    And should not we be sucked into the void?

Panel 2:
Tech: My instruments show no reading at all, other than slight power fluctuations. This is puzzling.
Engineer: What if we shoot into it?
Tech: Why?
Engineer: To see if it's real.
Tech: But won't that--
Engineer: Nah. A low setting will be absorbed by the wall.
Tech: Perhaps we should ask Glugtor if--
Lieutenant McDougal: Okay, this is a problem! Shouldn't they be seeing a bulkhead?!
Ensign Yuna: The cloak doesn't work like that! It's meant to be used in space!
    And there's a bigger problem... the shuttle hatch is jammed open!
McDougal: All right, then we need to--

Panel 3:
Tech: What... humans?!
Engineer: So much for our Blurz session.
    It's a cloaked shuttle! We have been boarded!
    Hit the alarm! Get reinforcements!
Yuna: Ungh!!

Panel 4:
SFX: CLANG CLANG CLANG!!!
Colonel Hank Reynolds: That can't be good.

Panel 5:
Tajaran Soldier: Foolish humans! Throw down your weapons!

Panel 6:
McDougal: Colonel, I know you said text only, but we have a problem!
    They found our shuttle! Yuna is down! We can't hold it!

Panel 7:
Hank: Do whatever you have to, Lieutenant!
    We're having our own problems!

Panel 8:
Major Ulbek: Our body armor will not last long, sir!
Hank: We need to get out of this hallway!

Panel 8:
Ezzok: I've got one grenade round this thing!
    Good time to use it?
Hank: You mention this now?! Yes! Fire that thing!