The Services have a language all their own, and most of it has found its way into everyday life: Some more:
"Wait till you see the whites of their eyes."This was coined by ships' gunners in Nelson's time.Ship to ship bombardment took place in close proximity, and while the ship's guns had no sights nor any mechanical means of judging distance, experience dictated that at 400 yards it was possible to hear conversation on an opponent's ship, and at 200 yards the white's of the enemy's eyes could be seen.
"Three sheets to the wind"Also from the RN, this is a sailing term when the ship, through poor setting of sail, veers and luffs almost out of control. Just like a Dining-out!