The spear analogy dates at least as far back as 1940. Heavy mechanized units as the tip and then reinforcing units behind them, further units to secure flanks, logistics flow. From the metal differences across the head of a spear (something that people who have a passing familiarity of artillery or naval gunnery will be able to relate to) the finish of the handle to keep the wood in good shape the analogies basically write themselves. The dick jokes are an obvious follow on.