UK, 1805—personifies France or the French people, or designates a typical Frenchman—composed of ‘Johnny’, a pet form of ‘John’ used, with modifying word, to designate a person of the type, group, etc., specified, and of French ‘crapaud’ (a toad)—coined by British sailors during the Napoleonic Wars
UK and USA, 1816—to tell a long, far-fetched story—of nautical origin? (perhaps alludes to making ropes from lengths of yarn on board ship: the men would have told one another stories while performing this long and tedious task)
USA, 1812—UK, 1818—the name of a character proverbially said to have been so great a liar that he was expelled from Hell—hence, frequently in ‘a bigger liar than Tom Pepper’, and variants: an outrageous liar
literal meaning (1551): halfway across the sea—figurative meanings (1692): halfway towards a goal or destination, half through with a matter, halfway between one state and another—also (1699): half drunk
UK, 1870—a very hard ship’s biscuit—refers to the fact that these sea-biscuits were particularly carried by Liverpool merchant ships; likens the shape and hardness of these sea-biscuits to those of pantiles, i.e. roofing tiles curved to an ogee shape
1922—nautical—figuratively, means that different countries (or cities, spheres of activity, etc.) have different customs or practices—‘long splice’: a splice in which the ends of two ropes are interwoven in such a way that the point of joining and the ropes are of equal thickness
UK and Ireland—with reference to the fact that Horatio Nelson was blinded in one eye—(1922) ‘until/when Nelson gets his eye back’ is used of a very long time in the future—(1933) the metaphor of Nelson getting his eye back is used of a very small chance of success
UK, 1808—to make one’s beliefs or intentions plain—from the former practice of nailing an ensign to the mast of a ship, after damage during battle resulted in the ship’s colours no longer being clearly displayed, which otherwise might have been interpreted as a signal of surrender
applied to someone who will drink anything—UK, 1790—from the tale of the sailor(s) who stole spirits from the cask in which a dead Admiral was being preserved for interment in England