Their principal functions, theoretically, are to discover and kill the enemy's torpedo boats, guard and scout for the main squadron, and perform messenger service. However, they are also torpedo boats of a most formidable kind, and in action will be found carrying out the torpedo boat idea in an expanded form. Four destroyers of this type building at the Yarrow yards were for Japan (1898).
The modern European ideal of a torpedo boat is a craft 152 feet long, with a beam of 15¼ feet. When the boat is fully loaded a speed of 24 knots is derived from her 2000 horse-power engines. The destroyers are twin screw, whereas the torpedo boats are commonly propelled by a single screw. The speed of twenty knots is for a run of three hours. These boats are not designed to keep at sea for any great length of time, and cannot raid toward a distant coast without the constant attendance of a cruiser to keep them in coal and provisions. Primarily they are for defence. Even with destroyers, England, in lately reinforcing her foreign stations, has seen fit to send cruisers in order to provide help for them in stormy weather.
Some years ago it was thought the proper thing to equip torpedo craft with rudders, which would enable them to turn in their own length when running at full speed. Yarrow found this to result in too much broken steering gear, and the firm's boats now have smaller rudders, which enable them to turn in a larger circle.
At one time a torpedo boat steaming at her best gait always carried a great bone in her teeth. During manœuvres the watch on the deck of a battleship often discovered the approach of the little enemy by the great white wave which the boat rolled at her bows during her headlong rush. This was mainly because the old-fashioned boats carried two torpedo tubes set in the bows, and the bows were consequently bluff.
The modern boat carries the great part of her armament amidships and astern on swivels, and her bow is like a dagger. With no more bow-waves, and with these phantom colours of buff, olive, bottle-green, or slate, the principal foe to a safe attack at night is bad firing in the stoke-room, which might cause flames to leap out of the stacks.
A captain of an English battleship recently remarked: "See those five destroyers lying there? Well, if they should attack me I would sink four of them, but the fifth one would sink me."
This was repeated to Yarrow's manager, who said: "He wouldn't sink four of them if the attack were at night and the boats were shrewdly and courageously handled." Anyhow, the captain's remark goes to show the wholesome respect which the great battleship has for these little fliers.
The Yarrow people say there is no sense in a torpedo flotilla attack on anything save vessels. A modern fortification is never built near enough to the water for a torpedo explosion to injure it, and, although some old stone flush-with-the-water castle might be badly crumpled, it would harm nobody in particular, even if the assault were wholly successful.
Of course, if a torpedo boat could get a chance at piers and dock gates they would make a disturbance, but the chance is extremely remote if the defenders have ordinary vigilance and some rapid fire guns. In harbour defence the searchlight would naturally play a most important part, whereas at sea experts are beginning to doubt its use as an auxiliary to the rapid fire guns against torpedo boats. About half the time it does little more than betray the position of the ship. On the other hand, a port cannot conceal its position anyhow, and searchlights would be invaluable for sweeping the narrow channels.
There could be only one direction from which the assault could come, and all the odds would be in favour of the guns on shore. A torpedo boat commander knows this perfectly. What he wants is a ship off at sea with a nervous crew staring into the encircling darkness from any point in which the terror might be coming.