Besides the house signals there are some generally accepted signals used by all vessels. A blue light is the signal for a pilot in all waters, except those of the United States. It is curious, however, that no universal pyrotechnic signal of distress has yet been arranged, although in 1889 Mr. F. Crundall endeavoured to get a standard distress signal recognised by shipping throughout the world. This signal, which consisted of a Roman candle surrounded at the mouth by four lights which burnt simultaneously with it, was demonstrated before the Board of Trade, and was distinguishable across the Channel at Dover, but was, however, not universally adopted.
Another extensive field use of pyrotechnic signals at sea is in the fishing industry. Lights and rockets are used to communicate between vessels of the fishing fleets and with the carriers.
The use of such signals by the coastguard and the Lifeboat Institution and at harbours and ports throughout the world is also very great.
Another pyrotechnic store of the greatest utility is the line-carrying rocket, a device which has been responsible for the saving of thousands of lives.
The credit for suggesting this use of the rocket appears to belong to a Mr. Trengouse, of Cornwall. This was in 1807. The proposal did not, however, make as much headway as it should have done, owing to the fact that Capt. Manley had that year introduced a device with a similar purpose, the line being carried by a shot fired from a mortar. This idea had been previously worked out by a Sergt. Bell of the Royal Artillery and by La Fère, a Frenchman, the two working independently.
The Manley apparatus was officially adopted, and stations established at forty-five positions round the coast.
The rocket method was, however, revived in 1826 by a Mr. Dennett, of Newport, Isle of Wight, and four stations were established on the island for the use of rockets of his pattern. The advantages of the rocket over the shot apparatus are obvious—the lightness and mobility of the rocket trough as compared with a mortar, the fact that the rocket traces its own flight, which can be seen and followed even at night, not to mention greater simplicity in working. However, it was not until 1855, when a rocket of greater range was invented by Col. Boxer, of the Royal Laboratory, that the rocket as a line carrier came into its own.
The Boxer rocket consisted actually of two rocket cases joined head to tail, and so arranged that when the first case had burnt out it was blown off, and the second gave renewed impetus. This rocket is still in use at the Board of Trade rocket stations.
A further development of the line-carrying rocket which is making rapid headway is a compact apparatus designed for use on the wrecked vessel to carry a line to the shore.
This system has two great advantages, namely, the target is so much greater when firing from the ship, consisting as it does of the whole coast line, whereas the ship forms in comparison an insignificant mark from the shore. Again, a vessel is generally wrecked on a lee shore, so that in firing from the ship the rocket travels with the wind.