The quote from Rudyard Kipling's "Screwguns" gives the game away. You have found an artillery drag rope c. WWII. The hook with leather strap is usually put through the 'eye' on the wheel hub, the leather strap simply acting as a guard to prevent it bouncing out between heaves.
The other end with the two chains has an interesting purpose: the 25, 6 and 17 pounders all had small metal cleats welded to the outside edge of the wheel rim... the small loops at the ends of the chains could be hooked over the two lowest cleats and the rope passed vertically to the top most cleat and then horizontally to the detachment. On heaving, the rope acted as a lever with the topmost cleat as the fulcrum thus rotating the wheel towards the heaving detachment (its hard work and can lead to the "heaves" as well!
). This technique was useful in deep mud and was a variation on drills from the wooden spoked wheel days. Modern gunners have forgotten this useful technique and simply jump into the bog and try to push on the slimey wheels! Our grampas weren't so dumb!
Before you part with it (if such is your plan) please post the length as I am making some up right now and am missing that small piece of info.
Ubique!
Mike