THE HAIIBOTJRS OF NEW ZEALAND.

11

A.—No. 4

Enclosure in Ko. 9. Extract from the Globe. Last year Sir W. Armstrong wrote a remarkable letter to the Times on our Harbour Defences. He there urged in the strongest manner that some means should be taken for affording protection to our open seaports. He pointed out that, in the case of Liverpool, a single hostile ironclad might do incalculable mischief, destroy masses of merchantmen closely packed in docks, and burn large stacks of warehouses containing merchandise worth millions. The remedy proposed by Sir William Armstrong was a system of floating gun-carriages, each mounting a heavy rifled gun. He referred to the little " Staunch" as an example, pointing out that this vessel, although a mere barge, carried a 250-pounder rifled gun of twelve tons weight, was quick and handy under steam, drew very little water, and was at a distance such a dot on the water that she would bo very difficult to hit; whereas her shot would plump every time into the side of any large sea-going ironclad. We remarked in our comments at the time, that it was evident the safety of many of our seaports depended merely on the forbearance of an enemy, and that it was absolutely necessary to make our harbours secure against a sudden dash of the nature contemplated by Sir William Armstrong. We further pointed out that there did not appear to be any difficulty in constructing a hornet fleet, each vessel of which should carry a 10-inch muzzleloading rifled gun, capable of sending a 400 lb. Palliser shell slap through the side of any foreign ironclad at 1,000 yards. We have reason to believe that a certain number of these useful little vessels carrying these guns will shortly be afloat; but we know that considerable difficulty has been experienced in stowing away so large a gun as the 10-inch of 18 tons. It is satisfactory, therefore, to find that Captain Moncrieff has devised a plan of raising and lowering such a heavy gun, so simple in its operation that it has received the approval of Sir William Armstrong and Mr. Rendall, the designer of vessels of the " Staunch" class. Captain Moncrieff has called his arrangement a hydro-pneumatic carriage, in which the recoil of the gun is absorbed by pneumatic agency. The principle upon which it depends is that the elasticity of air provides the most perfect spring that can be conceived. When out of action, the Moncrieff gun is safely stowed away below the deck. To all appearance the wasp becomes an ordinary fly; its sting is hidden. Suddenly, however, the huge monster rises from his lair, shows his black muzzle for a moment over the bulwark, vomits forth a stream of fire, and slowly descends out of sight. The gun is mounted on a simple but wonderfully ingenious carriage. The recoil, as the gun descends, drives a plunger into a cylinder filled with water, and communicating by a pipe with a reservoir, the lower half of which is filled with water and the upper half with air. The latter is thus compressed, and becomes a spring sufficiently powerful, when released, to return the plunger, and consequently the gun, to its original position. The air-spring is eased by a simple stop-cock, which permits some of the water to escape past the plunger. It is easy to see that this system possesses many of the advantages of the turret system, while it is free from many of its defects. The gun in the firing position is exactly in the same relative position to the deck of a vessel as it would be in a turret. In the latter, however, it is always obliged to remain at the same level, and thus requires a heavy circle of wrought iron above the deck to protect its carriage and gun detachment. In the loading position the Moncrieff gun is safe below the deck, and throroughly protected by the sides of the vessel. It is worked with greater ease and freedom on the lower deck than it could be in any turret, and it can be fired from under cover and at any elevation required. The extra weight of a turret is about 170 tons top-hamper, but a Moncrieff 25-ton gun would only require 16 tons additional weight, and none of this would be top-hamper. When the gun is fired it descends into the loading position by the recoil, under cover —if necessary under the water-line. The force of recoil is not lost but stored; and the simple operation of turning a cock raises the gun at once, and under perfect control, into firing position. The carriage appears of the simplest construction, and all the hydraulic appliances are stowed away in safety at the bottom of the vessel. Finally, Captain Moncrieff is encouraged and backed up by such men as Major-General Sir Lintorn Simmons, E.E., Sir W. Armstrong, Mr. Rendall, and many other distinguished engineers. We trust, therefore, that no time will be lost in giving this system a fair trial, particularly in vessels of the " Staunch " class. The invention is of such a simple and practical form that there is every probability of its success; and the Admiralty may rest assured that one of the first questions next Session will be, " Has Moncrieff's pneumatic carriage been tried yet?" If the answer is in the negative, it will only be a fresh proof that something must be done to thoroughly arouse the masterly inactivity of Whitehall.

No. 10. The TTicdee Seceetary for Defence to Lieut.-Colonel Cabgili.. Sic,— Colonial Defence Office, Wellington, 14th July, 1871. I have the honor, by direction of Mr. Eox, to acknowledge the receipt of your letter of the 6th instant, conveying your remarks upon Captain Hutton's report on the harbour defences of Auckland, and making suggestions for the defence of the harbour of Port Chalmers, and to thank you for the same. In reply, I am to Btate that Captain Hutton has been requested to report in a similar manner upon the harbours of Lyttellou and Port Chalmers; and his reports, together with your letter under reply, will be printed and laid before the General Assembly for its consideration. I have, &c , Lieut.-Colonel Cargill, Commanding Militia District, G. S. Coopeb. Dunedin. 3