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before noticed, modern progress doubles that distance; nay, Sir W. Armstrong deposes, that “for special service, guns might be constructed to give a range of six miles, or perhaps more,” and the committee, on the effect of the new rifled-cannon on fortifications, inform us that it will now be “necessary that an enemy be kept at a distance of 9000 yards, or five miles,” and that thus “a place situated on a flat, or surrounded by heights that look into it from that distance, would require a contour of outworks upwards of thirty miles in extent.”

There is another point to be borne in mind in considering the effect of the modern method of warfare, at least as far as a sea attack is concerned. Our heaviest ordnance are placed, and with reason, on gunboats. A very few of these, armed with a couple of the new rifled-cannon each, and firing conical shell, would be sufficient to set all Portsmouth dockyard in a blaze at a distance of four miles, whilst at that distance each gunboat presents but a tiny mark for the batteries on shore. Nor is this all. The plan of action with gunboats is—as at Sweaborg—to keep constantly in motion, generally circling round and round, easing for a moment as the gun is ready, delivering fire, and then steaming on again during the reloading. To hit so small an object under such circumstances is, as has been observed, extremely difficult. No wonder that Sir Wm. Armstrong considers that “at 4000 yards a gunboat would be practically safe.”

The principle of modern defences, therefore, is necessarily no longer a complete enceinte, as in old days, by which the place to be protected was surrounded by a cunningly devised system of ramparts and ditches, so arranged as that the various parts mutually supported each other; or rather, it is not only this, for the old ramparts are still good for close fighting, but it consists principally in pushing forward to a sufficient distance, in advance of the place to be defended, a series of detached forts, or “out-works,” as they are called, so arranged as at once to be each a little fortress in itself, and at the same time assist its neighbours on both sides with that most terrible of all artillery appliances—a cross-fire. Through a well arranged cordon of such works, it would be impossible, or nearly so, for an enemy to push his way on land, at least without first reducing them; and whether at land or sea, even a successful dash through them, without reducing them, would leave the advancing force open to attack in the rear. In some cases, as we shall see presently, it is deemed advisable to connect these detached works by lines; but the principle remains the same.

It has been necessary to explain at length this principle of modern fortification, because, without some comprehension of it, it would be difficult to understand the full object of the seven-and-twenty detached forts, with which in our engraving the country round Portsmouth appears dotted; whilst with such a comprehension, the system becomes the simplest thing in the world.

A land attack on Portsmouth would be made either from the west or from the north; the first, by an enemy who had landed somewhere west of the Needles, for, as we shall presently see, the passage of the western entrance of the Solent by a force of troops and artillery sufficient to effect a landing between Southampton Water and Stokes’s Bay, may be looked upon as an improbability, nearly amounting to an impossibility; the other, by an enemy who had landed either on that spot or eastward of Langston Harbour, with a view of marching on London, and who should either attack Portsmouth as his first step, or detach a portion of his army to destroy it, whilst his main body kept our force in the field in check.

The advance from the westward would meet with the triple line of defence presented by (1º)