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Appendix No. 4.

DIEGO GARCIA.

strong the superstructure, shot and shell would penetrate deeply into the foundation, and shake to pieces anything built on it. But, supposing a battery placed there, would it be effectual? I can hardly think so, without the mines. A ship steaming 10 knots could run in at a clear distance of 2,400 yards, and be only under fire for six minutes. Of course, the presence of mines alters the case; but then there is the eastern passage, and unless the mines proposed for its security were also under the effective fire of a battery on shore or afloat, they would be surely destroyed. It is, I submit, an axiom that mines should not be laid unless covered by artillery. Hence the West Island battery would entail the necessity of another on North-East Point, or the constant presence of a gun-boat. For these reasons I have come to the conclusion that, if a refitting station or coal depôt is to be formed, and protected by shore batteries, those defences should be at the sites selected, and not at the entrance. ·

Reverting now to the site A,* to which I have alluded as the best for a refitting station, I would point out that a casemate battery on East Point would thoroughly guard the passage into the lower portion of the harbour. The channel is broken by several patches, and therefore better adapted for defence. No central island or islet exists, and in the direction indicated on tracing I would lay mines. But the position would have to be protected from land attack; earthworks would have to be thrown up across the land north and south, and a couple of heavy guns placed on the east side to ward off a bombardment in that direction. And in the case of the site B,* selected as a simple coal depôt, works of any strength might be erected according to the importance to be attached to the place; but as the telegraphic instructions alluded to such defence as might cope with a small squadron, I apprehend that no very extensive works were anticipated. Yet there seems but little use in any defence unless capable of withstanding an attack from iron-clads carrying very heavy guns, since it is that class of ships that stand most in need of coaling-stations; yet to prevent such ships being supplied from the station by means of fast steam-ships acting as tenders, I would recommend two batteries, each for two 6-ton guns, the one at the north and the other at the south of the station; a third battery, for another 61-ton gun, or one 8-inch breech-loading rifled gun, to be placed at the rear of the position, near the west coast, to ward off a bombardment from the sea side; and on the enceinte, which should consist of a musket-proof wall, with a moderate ditch outside and a banquette inside, I would mount three 64-prs. for land defence. I attach a tracing of the sort of work described, which would, I think, be sufficient to prevent an attack from any but formidable ships. Such a work would require a garrison of about 100 men, including 50 gunners.

#

Now, as to the cost of such works, I feel that the only clue I can give must be through descrip- tion of the place. I can form no idea what the cost of the land would be, what the price of provisions and materials imported, because I am not in a position to say from whence they would come. Every- thing required for the works except lime, coral, and water would have to be supplied from elsewhere. The place is too hot for Europeans. Artificers, masons, and carpenters would probably have to be brought from Madras. If there is any precedent for such works, the expenses then incurred might form a general guide, but so completely am I without the most necessary data to work on that I feel I have no doubt that the officers at the War that any figures I might give would be apt to mislead.

Office had some good grounds for the estimate given for the works proposed, and if such works as I have alluded to herein seem worthy of consideration, a comparison of the natures of these works would lead to some idea as to the cost of the latter. But I cannot conclude without expressing my opinion that it is a fatal mistake to erect any fortifications on such a place, and I venture to think that too much importance has been attached to it from its position. It has been stated in the War Office Admitted; Memorandum that it is in the direct route of vessels outward bound viâ the Cape to India. but what does that trade consist of? The trade round the Cape is almost exclusively carried on by sailing-ships. Almost the whole of the Indian steam trade passes through the Canal. Now to sailing- ships Diego Garcia will never be a desirable port. It is only visible at a very short distance, and lies too close to the sunken reefs of the Chagos Bank and Peros Bank to be a pleasant locality in thick weather. The winds, too, are variable, and strong currents exist. When returning to Ceylon we experienced so strong a westerly current setting towards the Chagos Bank that it became necessary to make a change of course during the night; and then, as regards steamers, should a trade arise, or the canal be closed, would they not prefer to select a port half way between the Cape and Ceylon as much in the direct line where there is a commodious harbour well protected by batteries, a port where provi- sions can always be had, dock exists, and repairs can be effected. Again, as to its being a refitting station for our navy in the East, what advantages does it offer? I do not believe a dock could be built there; no provisions can be obtained; everything wanted would have to be brought there, and it is I do not think that I am speaking quite out of the line that any of our ships usually take. inaccurately when I say that, with the exception of the "Fly," which unintentially visited the island in 1873, no ship of our navy has sighted the island from the time of the survey of 1837 until the 10th June last.

It is, on the other hand, easy to see why the Orient line should wish to utilize it. It lies one- third of the way on their course from Aden to Cape Leewin. They could supply themselves with coal cheaper there than they could at Aden, and could set a couple of hundred tons of space at liberty for cargo, but, so far as I can see, the place is only of use to ships taking that particular track.

If we

Well, then, if the trade on that line becomes very great, may not that be a reason for having a refuge and protected port for such ships to run for and recoal in time of war? I think not. were engaged in a naval war it would be as well for ships requiring supplies or protection to run for Trincomalee, which must eventually be made absolutely secure, and which would not delay their passage more than two days.

It will not, I think, be maintained that it is desirable to establish a new military station for the sake of shortening the passage to South Australia in time of war by one or two days. But before I leave this subject I must point out that, however useless to us the place seems to me for war purposes, its possession by an enemy might be of great importance. If strongly fortified and made the rallying * Plan not printed.

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