It was the evening of 22nd April 1778, and John Paul Jones' sloop-of-war, the USS Ranger, was standing off Whitehaven harbour in the darkness of a rather cold spring night. The plan was for Commander John Paul Jones to lead a small detachment of two boats from the USS Ranger, to raid the shallow port of Whitehaven, where, by his own estimation, 400 British merchant ships were anchored. Jones was hoping to reach the port at midnight, when the ebb tide would leave the ships at their most vulnerable. Each boat would head for one of the two forts guarding the harbour. Jones in one boat and, Lieutenant Wallingford of the US marines in the other, hoped to take both forts and then to set fire to all the shipping which would be helpless whilst grounded by the low water tide. John Paul Jones had instructed his cannoneer, who remained on board the USS Ranger, to fire at the Whitehaven Watchtower at midnight. Now this worried the cannoneer as it was a relatively small target to aim at, and at about a mile away, at the limit of the range of the his 18x6 pounder guns. He therefore set up the best of his cannons for maximum range and added a bit more gunpowder in the charge than normal. However, when the time came, he overshot the target of the Watchtower by some distance. He consoled himself that the direction was spot on and, with the southern fort ablaze, hoped that John Paul Jones would not be too disappointed.
Now modern technology, and maths, allow us to work out exactly where the small 6 pounder cannonball landed. The cannonball was fired with the initial speed of 120m/s. As stated above, the cannoneer had a precise bearing on Whitehaven Watchtower, just he overcooked the range. Go and find the cache where the cannonball landed. Now, for the sake of correctness, confession time; not all of the above is true. John Paul Jones greatly underestimated the strength of the ebbing tide and did not reach shore until almost dawn, far too late for his plan to succeed. He did however take, and set fire to the southern fort. Lieutenant Wallingford, legend has it, sloped off to the local pub to ask for a light and a swift pint without setting anything afire. Whilst this may be a bit of an urban myth (asking for a light and having a pint), the cannoneer's efforts to pound Whitehaven Watchtower is definitely a myth. It was concocted by the COs to get would be cache finders to do some sums.
So it only remains for you, dear cacher, to do the sums and go find it.
You can validate your puzzle solution with certitude.