One of the answers of the United States ordnance engineers to this problem, as developed in the recent war, has been the production of a tractor to replace the horse, and this tractor has the speed of the deer and the power of the elephant. The most powerful tractors are mounted on track-laying devices and are colloquially known as caterpillars. One of these powerful caterpillars, on which is mounted an 8-inch howitzer with a range of 6 miles, which is manned and operated by only two men, and which can go up hill and down hill, over broken brushwood, trees, etc., was recently given a severe test at the Aberdeen Proving Grounds. Here it was sent through a dense wood in which it bumped square into a live locust tree that was 17 inches in diameter at the bottom. This tree, almost the tallest in the wood, was prostrated by the attack of the tractor, which rode over it and then emerged from the wood, took up its position, and fired its shot almost in as short a time as that which it takes to tell of the deed. Truly the power of the elephant and the speed of the deer has been brought to the aid of the ordnance engineer for any future warlike operations. The number of workmen employed in gun production at once in this country totaled 21,329, and fully that many more are estimated to have been employed in the manufacture of gun carriages and fire-control instruments. Consequently in turning out the complete big guns there were fully 42,000 workmen engaged by the month of October, 1918. Furthermore, these men became so skilled in their work that it may be said that the difficult art of gun making has become firmly established in this country and that the United States may now and at any time in the near future rely on this trained body of artisans for the finest kind of gun-metal manufacture. PRODUCTION OF CANNON FORGINGS. _Production of cannon forgings during the war at the various plants._