For purposes of torpedo attack the periscope is used as a range-finder to determine the distance the target is away, and also in connexion with tables to determine the correct time to fire the torpedo, allowing for the speed of the enemy, course, etc. Officers of submarines have devised various mechanical devices to avoid calculations, and these have been added to the periscope.
The Portuguese navy in 1910 consisted of 1 armoured vessel, 5 protected cruisers, 2 third-class cruisers, 19 gunboats, I torpedo gunboat, 4 torpedo boats, 16 river gunboats, 4 transports and 3 training ships.
There is a torpedo and submarine boat station on the north side of the channel at the entrance to the lake, but the principal naval works are at Sidi Abdallah at the south-west corner of the lake and to m.
Over the sill at high water of spring tides; the construction of new jetties at the entrance to the tidal basin and at the north wall; the establishment of a coal wharf with hydraulic appliances; a torpedo range in the harbour; the erection of various buildings such as torpedo and gun-mounting stores, electrical shops and numerous subsidiary works; and extensive dredging of the harbour to increase the berthing accommodation for the fleet.
The term is also used of structures resembling these articles, especially of the framework of booms, spars and netting forming a protection for a warship against torpedo attack.
The navy, many of the officers of which are Danes and Norwegians, comprises a steel twin-screw cruiser of 2500 tons which serves as the royal yacht, four steel gunboats of between 500 and 700 tons all armed with modern quick-firing guns, two torpedo-boat destroyers and three torpedo boats, with other craft for river and coast work.
The navy consists of 6 small battleships, 3 coast defence armour-clads, 5 protected cruisers, 5 gun-boats, and 24 torpedo craft.
It consisted in 1905 of 9 modern battleships, 3 armoured cruisers, 5 cruisers, 4 torpedo gunboats, 20 destroyers and 26 torpedo boats.
Land was acquired and works were planned, but the development of possibilities of torpedo attack soon made it evident that the outer anchorage, as originally designed, would be insecure, and naval opinion became doubtful as to whether the base would be adequate.
The naval strength of the republic consisted in 1906 of a collection of armoured and wooden vessels of various ages and types of construction, of which three armoured vessels (including the two designed for coast defence), four protected cruisers, five destroyers and torpedo-cruisers, and half a dozen torpedo boats represented what may be termed the effective fighting force.