letion, 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mercantile losses were very heavy, some submarines were withdrawn from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