Extract from a letter written by William F. Drummond Jervois, Governor and Commander-in-Chief of Victoria, outlining defence solutions for Port Phillip.

DEFENCE IN PORT PHILLIP BAY, 1879

… The greatly increased power of artillery has led me also to consider, whether it would be possible, with a due regard to the object in view, to substitute batteries on land, for either or both of the works proposed to be erected on submarine foundations for the defence of the channels through the shoals of Port Phillip.

With respect to the South Channel, it should be borne in mind that this is the only passage by which ships of deep draught can approach Melbourne. The only site on land which can be suggested as a position for a battery for its defence is Point King, the north-eastern point of the peninsula which divides Port Phillip from the sea, and about five sea miles from the entrance. Ironclad vessels passing up this channel may, however, keep at a distance of nearly two miles from Point King; and I do not consider, – making due allowance for increased power of guns, – that reliance could be placed upon the artillery defence being efficient at this range. On the other hand, a ship must pass within 1,500 yards of the fort proposed to be constructed on the shoal near No. 5 buoy, and its artillery fire cannot fail to be effective. I am decidedly of opinion that this work should be carried out as soon as possible, and I recommend, as a first step, that a contract be forthwith entered into for the pierres perdues portion of its foundations.

As regards the superstructure, the massiveness of the work and the thickness of the iron front of the casemates should be such as to meet, as far [as] possible, the increased power of artillery, bearing in mind, however, that the powerful guns which it is proposed to adopt in the defence will be capable of preventing any armoured vessel likely to appear in Australian waters from engaging the fort, except at very distant range.

With respect to the defence of the West Channel, and other passages adjacent thereto, the plan proposed in my memo of July, 1877, was to construct, on the shoal between West Channel and Symond's Channel, a fort which, in conjunction with torpedoes to be placed across those channels, would not only prevent the passage of an enemy's vessel through them, but would also cover Cole's and Loelia Channels, the entrances to which are within the proposed line of defence.

In considering whether the recent increase in the power of artillery renders desirable any modification of this plan, it should be borne in mind that vessels passing through Port Phillip to Melbourne, if below a certain draught of water, always use the West Channel; if above that draught, they use the South Channel. Vessels never go through Symond's Channel; indeed that channel is so much obstructed by shoals that it cannot be considered navigable. It is true that a hostile vessel of light draught, if she were allowed to take her time and were unmolested, might pick her way through these shoals at two points, – one near the Middle Sand, the other at the outlet on the Melbourne side, – but, the channel being never used, these openings may be closed against an enemy by mechanical torpedoes in conjunction with floating obstructions and piles. It should be remarked that in passages which it is necessary to keep open for navigation, torpedoes intended for their defence must be worked by electrical agency, so that they may be innocuous, except when by the completion of the electric circuit they are rendered active for the purpose of stopping hostile vessels. In channels not used for navigation, however, mechanical torpedoes, which obstruct the passage to friend as well as foe, may be applied.

It will be seen that it is not necessary to construct a fort in the sea solely for the purpose of providing a close artillery fire upon Symond's Channel. It is, however, still essential that there should be an effective artillery defence for West Channel, and the question arises whether, under present circumstances, it is possible to provide this without placing a fort on the shoal between it and Symond's Channel. The main reason for originally proposing a fort there was that it is the site from whence the shortest range (not exceeding 1,500 yards) can be obtained upon West Channel. The increase in the power of artillery, however, renders it unnecessary to bring so close a fire to bear upon the passage. An examination of the chart will show, that a ship navigating the West Channel must pass within about 1,800 yards of Swan Island, and, with the new guns, a thoroughly effective fire may be afforded at this distance. I therefore recommend that a work be constructed on that island, in lieu of the proposed fort on the shoal between the West and Symond's Channels. In conjunction with the work, electric torpedoes should be placed across the West Channel. Torpedoes, which will be under the fire of the guns on Swan Island, should also be placed across the narrow entrance to Loelia Channel.

The work on Swan Island should be enclosed and rendered secure against assault, with barrack accommodation for the garrison placed in the rear, and arranged so as to form a "keep." The battery should be designed for five powerful pieces of ordnance sweeping the channel and two lighter guns at the gorge bearing on the flanks and rear. Three of the heavy pieces should be 10-inch guns of the new pattern, the other two may be 9-inch guns of the present service pattern, already in store in Melbourne. Two 80-pounders, of which nature of gun there is a considerable number in the colony, can be utilized for the positions in rear. All the guns should be arranged for the new plan of mechanical loading.

The torpedo depôt for the submarine defences of the channels should also be placed on Swan Island, a traverse being erected to cover the buildings from the view of an enemy.

With reference to submarine defences, I desire to draw special attention to the fact – as stated in my report of the 20th July 1877 – that torpedoes, in conjunction with forts, are essential to prevent the passage of hostile vessels to the inner waters of Port Phillip. The torpedo stores should, therefore, be provided as soon as possible. I may add that it is essential that the arrangements in connection with the torpedoes should be in the hands of officers of scientific acquirements, who, during peace time, will devote themselves to perfecting this branch of the defence scheme, and to training the torpedo corps (organised on the plan recommended in my report) to a knowledge of their duties. This important part of the defensive organisation must be entirely irrespective of any torpedo provision in connection with the naval defences.

As regards expense, the work on Swan Island will cost much less than a fort on the shoal near West Channel. On the other hand, the outlay on the fort defending the South Channel will be greater than was originally contemplated. The total sum of £350,000, which I estimated as the capital cost of works, armaments, and torpedoes for the defence of Port Phillip, will, however, suffice.

William F. Drummond Jervois, Governor and Commander-in-Chief of Victoria, written at Government House, Adelaide, 1 March 1879, SLV, MS 107908, Box 960/5.