It was the narrowest part of the straits, between Calais and Dover, which they most earnestly coveted. Calais was their great objective, and they had begun to boast of the victory which they felt certain they must soon achieve. They were already in possession of the Belgian coast. Their trenches were dug close to the sea, supported by their big guns concealed among the sand dunes. From the sea itself there could be no danger, since the water was too shallow to admit of British battleships coming within range, and, besides, the sea was thickly sown with German explosive mines.
It was in counting upon the shallowness of the water off the coast that they made their great mistake. No Dreadnought could come within range, it is true; but there are other vessels than Dreadnoughts capable of carrying heavy guns, though perhaps the Germans had not thought to find them off Nieuport.
The crew of the mine-sweeper Dainty had had their curiosity aroused by the sight of three peculiar-looking steamers flying the White Ensign, which came to anchor near them one Saturday evening.
Darby Catchpole was particularly interested in them. They were small vessels, of hardly more than a thousand tons. Their low hulls and their upper works, including the funnel and ventilators, were oddly painted in grey and white to confuse the eye and add to their invisibility.
"They look like river craft," said Darby. "I shouldn't wonder if they drew no more than four feet of water, even with the weight of their guns."
He was right about their being river craft. They had been built for the Brazilian Government for use in shoal water. Their sides were heavily armoured. Each mounted an armament of two 6-inch guns, two howitzers, four 3-pounders, and six quick-firing guns, and she could discharge a ton and a half of metal every minute.
These were the ships—monitors they were called—with which the British Navy was prepared to prove that the waters off the Flemish coast were not too shallow to admit of heavy guns coming within range of the German trenches. With their shallow draught they could defy the enemy's submarines, whose torpedoes were set to run about twelve feet below the surface, and they could move to and fro, confusing the aim of the Germans' heavy artillery.
The monitors were supported by several old cruisers, gunboats, and destroyers, French as well as British, and, much to the surprise of Harry Snowling and his crew, the trawlers also were ordered to take their part in the operations. They formed the advance guard to search for hostile submarines or possible mines, and to spy out the positions of the German batteries by drawing their fire, while the Allies' aeroplanes made observations from the air.
Suddenly the three monitors, coming within range, opened fire with their 6-inch guns and howitzers, and it was then that the Germans had the surprise of their lives.
Steaming backward and forward parallel with the coast, the ships kept up a constant cannonade, dropping their lyddite shells with precision into the enemy's trenches, smashing their batteries and spreading havoc and destruction.