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Appendix No. 4.

THURSDAY ISLAND.

These attacks best met by fixed and floating defences.

Objects to be gained by defences.

Relative importance and object of defence

measures.

Night attacks.

Details of defensive

measures.

*

3. He may, after forcing an entrance, occupy the place and fortify it, in order to establish a base from which to operate against Australian commerce.

4. Should he be unable to force an entrance, he may land at some convenient point, in order to command the anchorage with field-guns.

All these modes of attack can be best met and successfully resisted by a combination of fixed and floating defences, viz. :—

(1) Guns in suitable works on shore; (2) torpedo-boats; (3) a harbour defence gun-boat; (4) possibly submarine defences of a very simple and inexpensive character; and (5) an armed vessel

to act as a cruizer.

Two distinct objects have to be kept in view-the first being to secure the Settlement and coal depôt against a predatory assault; the second to provide means for the general defence of the strait, The first object will be served by the guns on shore, the gun-boat, and torpedo-boats; the second by the gun-boat, torpedo-boats, and armed cruizer. The employment of these floating defences will increase the first cost of securing Thursday Island and Normanby Sound against attack, and the annual maintenance of the defences; but the floating defences are indispensable, as the directions from which attacks could be delivered are so numerous and so scattered. Again, the smooth water which prevails in the Sound and channels is especially favourable to their use. Without them it would be impracticable to repel attempts by the enemy to land field-guns in order to take up positions from which the Settlement and anchorage could be fired into. The defenders' land force-if any were provided--could not prevent such an operation. At the same time, floating defences alone will not meet the case, as they are liable to be destroyed or disabled by artillery fire, or the action of torpedoes, consequently the provision of guns on shore to defend the Settlement and anchorage is absolutely

necessary.

The relative importance and the object of the several measures recommended may be recapitulated in the following order :-

1. Guns on shore to protect the Settlement, secure it from bombardment, and command the anchorage and approaches thereto.

2. Torpedo-boats to co-operate with the guns on shore by attacking the enemy's vessels as they approach, or whilst they are engaged in landing field-guns or men. They would also be available in the event of the guns on shore being silenced.

3. A gun-boat to assist in the defence generally of the anchorage and the several approaches to the Sound.

4. An armed cruizer for watching the strait generally, which would form part of the general measures adopted for the protection of Australian commerce.

5. Submarine defences might be included in the defence preparations whenever it was found

• practicable to do so; but they do not approach in importance the other elements of defence. An exception may be made in favour of suitable mechanical mines, which do not require the elaborate arrangements necessary for electrical mines. Speaking generally, the channels surrounding Thursday Island are not favourable to the employment of defensive electrical torpedoes of the stationary class. The great velocity, irregularity, and uncertainty of the tides, the nature of the bottom, the existence of coral reefs, must militate against their efficiency, and I am very doubtful whether they could be so applied as to be really reliable. I should much prefer, therefore, to look upon them as accessories of minor importance, which may be utilized in their simplest form. On the other hand, locomotive torpedoes, fired from the shore, might perhaps be employed under certain conditions; but where economy is a paramount necessity, it is not possible to contemplate the employment of aggressive torpedoes, except in the shape of spar torpedo-boats.

With regard to the liability to night attacks, the intricacies of the approaches to the Sound and anchorage would be a sufficient safeguard against such operations if conducted with ships; but they would afford no security against landings and assaults by torpedo-boats upon the floating defences and vessels anchored in the Sound. To repel these attacks special precautions would have to be adopted.

Next, as to the details of the defensive measures proposed. It has already been observed that the anchorage in Normanby Sound is so scattered, extensive, and accessible from numerous directions as to render it impractible to secure it from bombardment by fixed defences alone. The main channel from the westward passes between Goode and Friday Islands; it is free from obstruction and of great depth, and although its width is only 3,000 yards, and there are sites at the entrance on which guns could be mounted, batteries would be of little value, as submarine mines could not be employed, and a ship could therefore steam past the guns on shore at considerable speed. There are no doubt good positions for advanced works at Webb Point on Friday Island, and at Kate Point on Hammond Island. The channel opposite Webb Point is narrowed by the Ghibber Rock and other reefs north and south; torpedoes could also be more easily employed in the channel off Kate Point. Both these sites are, however, open to the same objections as the sites on Goode and Friday Islands, of being isolated and commanded from adjoining hills. Moreover, an inner defence would still be required on Thursday Island to cover the anchorage and the eastern approaches to it, as well as to secure the Settlement from assault. To establish inner and outer batteries would be very costly, and would require a large garrison. Such a plan of defence would be so scattered and disjointed as to render combined and mutually supporting action a practical impossibility. This being so, it is obvious that the topography of Normanby Sound is such as to unfit it for a harbour in which vessels might lie in security and refit. To deny its use as a coaling and provision depôt, it will suffice to occupy some convenient position overlooking the anchorage, and fairly commanding the several channels of approach."

This is the conclusion arrived at by the Inspector-General of Fortifications in the War Office Memorandum* already quoted, and I entirely concur.

• No. 106.

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