The laying of the North Sea mine barrage was not accomplished without very considerable delay, and many difficulties were encountered.  It was originally anticipated that the barrage would be completed in the spring of 1918, but owing to various defects in both British and United States mines which made themselves apparent when the operations commenced, due partly to the great depth of water as well as to other causes, a delay of several months took place; and, even when near completion, the barrage was not so effective as many had hoped in spite of the great expenditure of labour and material involved.  I have not the figures of the number of submarines that the barrage is thought to have accounted for, but it was known to be disappointing.

FLARES

In the late summer of 1917 flares were experimented with; they were intended to be used from kite balloons with the object of sighting submarines when on the surface at night.  Previously searchlights in destroyers had been used for this purpose.  The flares were not much used, however, from kite balloons owing to lack of opportunity, but trials which were carried out with flares from patrol craft, such as trawlers and drifters, demonstrated that they would be of value from these vessels, and when the Folkestone-Grisnez minefield was laid in November and December, 1917, it was apparent that the flares would be of use in forcing submarines to dive at night into the minefield to escape detection on the surface and attack by gunfire.

Manufacture on a large scale was therefore commenced, and during 1918 the flares were in constant use across the Straits of Dover.

ELECTRICAL SUBMARINE DETECTOR

The existence of this very valuable device was due to the work of certain distinguished scientists, and experiments were carried out during 1917.  It was brought to perfection in the late autumn, and orders were given to fit it in certain localities.  Some difficulty was experienced in obtaining the necessary material, but the work was well in hand by the end of the year, and quickly proved its value.

SUBMARINE AGAINST SUBMARINE

Prior to the year 1917 the only areas in which our own submarines operated against enemy vessels of the same type was in the North Sea, or occasionally in the vicinity of the Hebrides.  Grand Fleet submarines were used in the northern areas during 1916, and Harwich submarines operated farther south, but the number of underwater craft available was insufficient for any extended method of attack.  Early in 1917, when our mercantile losses were very heavy, some submarines were withdrawn from the Harwich and Humber districts and formed into a flotilla off the coast of Ireland for this form of operation.  Some risk had to be accepted in thus reducing our submarine strength in southern waters.  At the same time some Grand Fleet submarines were organized into a watching patrol in the area off the Shetland Islands, through which enemy submarines were expected to pass.  The watch off the Horn Reef and in the Heligoland Bight, which had previously been in force, was also maintained.