Although the Stella Rigel and her sister sweepers must be constantly vigilant for some new form of mining offensive, the modern submarine mine is not a new invention so much as the product of four centuries of human ingenuity. During that time the scientists have fought an unceasing conflict of wits as one has produced a destructive device and another has countered it.

It was one of Elizabeth's admirals, Sir William Monson, who first realized that a vessel is more vulnerable below the water-line than above it, although there is no record that he ever carried out his plan for firing a cannon from the hold of a barque which had been laid alongside an enemy ship. But at the siege of Antwerp in  1585 the Dutch destroyed 800

Spaniards by means of a contrivance they called an " explosion vessel" fitted with clockwork mechanism.

Charles I gave his Master of the Ordnance a warrant " for the making of divers water-mines, water-petards and boats to go under water," and during the expedition for the relief of La Rochelle in 1628 the Duke of Buckingham, then Lord High Admiral, is said to have used these inventions, although without much success. In Cromwell's time Prince Rupert tried to blow up Blake's flagship, the Leopard, with an explosive machine concealed in an oil-barrel. Twenty years later he was still experimenting with " petards."

" Whatsoever vessel lies by the side of any ship and has the said petard on board, has it