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Appendix No. 4.

DIEGO GARCIA.

boats on account of the rapid shoaling of the water immediately inside the islands, and the innumerable patches of coral that nearly approach the surface.

The third pass, between Middle and West Islands, is the deep and safe one. These passes do not possess sufficient natural advantages to render it advisable to attempt their defence. A battery on Middle Island would be so retired, on account of the outlying reef, as to lose its most effective fire, and one on West Island would operate very ineffectually against a ship passing on the farther side of the channel, which is 2,500 yards wide. West Island, too, is a very small place, not much more than 2 or 3 feet over high water, and incapable of ever being made the key of the harbour, more especially as the eastern entrance, though exceedingly dangerous, is in moderate weather possible. Torpedo defence I consider out of the question. It would never be recommended to lay mines in such a place without having effective batteries to cover them. Hence the defence of the coaling depôt or naval station must be local and specially suited to the particular site selected.

The accompanying tracing* from the Admiralty chart, as corrected under your orders by Lieutenant Cuddy, R.N., shows the length and width of the land and the position of the shoals, but of course gives no idea of the flatness of the ground. The island is an atoll consisting wholly of coral. No natural formation appears anywhere. The coral, commencing on the summit of some submarine mountain peak, has gradually ascended to the surface of the ocean, until finding itself no longer washed by the daily tides, it ceased its upward growth. On the reef so formed innumerable shells have been washed up, plants and trees have grown and shed their leaves and died, and so raised the surface to its present height. It may be 4 or 5 feet above water. So low is the land that were it not for the broad reef which extends all round it, the heavy sea swell running up from the south-east during the greater portion of the year would wash right over it; this outer reef, however, gives it ample protection. It is now covered with abundant vegetation, the chief trees being cocoanut, of which there are upwards of 1,000,000.

This exceeding flatness places land defences at a great disadvantage, and the narrowness of the land and the great depth of the water close outside add considerably to the difficulty of harbour defence.

Now, applying these considerations to the establishment of a naval station, it would be advisable, in the first place, to mount all the guns in casemates protected by shields, inasmuch as batteries à fleur d'eau could not contend against ships of any considerable power, unless under cover and so protected. Again, it would be well to select a site where the land was so wide as to afford room for the require- ments of the station and due protection from bombardment from the sea side, and to these must be united such a depth of water close in to the land as to admit of ships approaching a wharf or entering a dock, should it be possible to construct one.

I venture to think that the only possible place for a refitting station where a ship could lie in calm weather at all seasons sufficiently close to the shore to be able to carry on repairs, would be at the point marked A on tracing,* just round the head of East Point. A large casemate battery should then But occupy the point at the promontory as indicated. Such a battery would require heavy guns. such a battery would not insure the safety of the station. Men could be landed elsewhere out of range, and a land attack made on either side. This could only be withstood by a sufficient garrison, and by running earthworks across the land above and below. Now, when I consider the great distance the place is from India, and the usual stations of the East India Squadron, the excessive difficulty of maintaining an establishment in so isolated a place, and the great difficulty there is in obtaining the services of a sufficient garrison to man places of undoubtedly greater importance, I cannot but feel that I am only wasting time in considering the subject further, and that I must give it as my opinion that the place is wholly unsuited to the requirements of a naval station.

I now come to the question of providing defence for a coaling depôt. All doubt as to the soundings being now removed, a glance at the chart shows what an excellent anchorage the harbour affords. You, Sir, in your Report, have doubtless given the reasons which led you to coincide with me in considering the place marked B on tracing* as the most suitable. I arrived at that conclusion because the width of the land and its proximity to the entrance gave, cæteris paribus, to this part of the island a decided superiority; then there, it seemed to me, it would be particularly easy to run out a pier along the flat reef, which is nearly dry at low water, to a point some 150 yards off where barges could be laden at any state of the tide.

The fact, too, that the eastern branch of the island forms a breakwater during the south-east trade, and that the heavy sea which rolls into the harbour from the north-west during the months of December, January, and February, sets to the eastward of a line joining West Island and Point Marianne, was, of course, one of the primary reasons for selecting that particular site.

I may here mention that the distance to the East Point and the intricate navigation leading into the waters beyond, which I am aware were fully considered by you in weighing the relative advan- tages of sites for coaling, did not seem to me to operate in the case of a naval station. Time in that case could not be so much an object as perfectly calm water, easy access to the shore, and other con- siderations.

Assuming, then, that the Site B be selected, I am asked how I would propose to defend it against the attack of a small squadron. I reply that I do not consider that any small works such as it is at all probable would ever be erected to meet such an attack would give adequate security, and that what may not be done thoroughly had better not be done at all.

Assuming, however, that the small squadron does not carry any heavier guns than 6 tons, and that none of its ships are armour-plated, I would recommend two 6-ton gun batteries for two guns each about 700 yards apart on the shore-line above and below the depôt. A third battery for one gun, about 400 yards in rear, to prevent a ship standing in close to the land and shelling the position from the sea-side. Also, I would provide two guns of less metal intermediate between the rear and front

* Not printed.

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