Germans of a delay action device in their mines, which caused them to remain at the bottom for varying periods after being laid.  The ordinary mine-sweep, the function of which was to catch the mooring rope of the mine and drag the mine clear of the channel, was, of course, ineffective against the mine on the bottom, and there was no guarantee that mines might not be released from the bottom and rise to a depth at which they were dangerous, after the channel had been swept and reported clear.  To deal with this danger a chain-sweep to work on the bottom was introduced, but its use presented many difficulties, especially over a rocky bottom.

When a regular swept and buoyed channel was in use the enemy had little difficulty in deciding on the positions in which to lay mines by reason of the presence of the buoys.  This fact constituted the principal disadvantage in the use of a buoyed channel, but in certain places where the traffic was heavy the procedure was inevitable, and it greatly simplified the work of the patrol craft and minesweepers; the only precautions possible lay in the use of alternative marked channels, and in the laying of defensive deep minefields outside the channel in which enemy submarines might compass their own destruction.  As rapidly as our supply of mines admitted, this latter device was adopted in positions where the minefields could not constitute a danger to our own submarines.  False buoyed channels with mined areas round them could also be laid in which to catch the submarine.  Another device was that of altering the position of light vessels and buoys with the object of putting a submarine on to a shoal.

The situation with which our patrol and minesweeping craft had to deal having now been stated, it remains to speak of the magnificent manner in which they accomplished their task.

I regret very deeply that, in spite of a strong desire to undertake the task, I have neither the information nor the literary ability to do justice to the many deeds of individual gallantry, self-sacrifice and resource performed by the splendid officers and men who manned the small craft.  No words of mine can adequately convey the intense admiration which I felt, and which I know was shared by the whole Navy, for the manner in which their arduous and perilous work was carried out.  These fine seamen, though quite strange to the hazardous work which they were called upon to undertake, quickly accustomed themselves to their new duties, and the nation should ever be full of gratitude that it bred such a race of hardy, skilful and courageous men as those who took so great a part in defeating the greatest menace with which the Empire has ever been faced.

There are, however, just two cases in 1917, typical of many others, which I cannot forbear from mentioning.  The first occurred off the East Coast of England.

On August 15 the armed fishing craft Nelson and Ethel and Millie were attacked by gunfire by a German submarine on the surface at a range of four to five miles.