partly the business of the Anti-Submarine Division of
the Naval Staff and partly that of the Operations Division); _defensive_
in the direction of protective measures for trade, whether carried in
our own ships or in ships belonging to our Allies or to neutrals, this
being the business of the Trade and Mercantile Movements Divisions.

Prior to the formation of the Mercantile Movements Division the whole
direction of trade was in the hands of the Trade Division of the Staff.

The difficulty with which we were constantly faced in the early part of
1917, when the effective means of fighting the submarine were very
largely confined to the employment of surface vessels, was that of
providing a sufficient number of such vessels for _offensive_ operations
without incurring too heavy risks for our trade by the withdrawal of
vessels engaged in what might be termed _defensive_ work. There was
always great doubt whether any particular offensive operation undertaken
by small craft would produce any result, particularly as the numbers
necessary for success were not available, whilst there was the practical
_certainty_ that withdrawal of defensive vessels would increase our
losses; the situation was so serious in the spring of 1917 that we could
not carry out experiments involving grave risk of considerably increased
losses.

On the other hand, the sinking of one enemy submarine meant the possible
saving of a considerable number of merchant ships. It was difficult to
draw the line between the two classes of operations.

The desire of the Anti-Submarine Division to obtain destroyers for
offensive use in hunting flotillas in the North Sea and English Channel
led to continual requests being made to me to provide vessels for the
purpose. I was, of course, anxious to institute offensive operations,
but in the early days of 1917 we could not rely much on depth-charge
attack, owing to our small stock of these charges, and my experience in
the Grand Fleet had convinced me that for success in the alternative of
hunting submarines for a period which would exhaust their batteries and
so force them to come to the surface, a large number of destroyers was
required, unless the destroyers were provided with some apparatus which
would, by sound or otherwise, locate the submarine. This will be
realized when the fact is recalled that a German submarine could remain
submerged at slow speed for a period which would enable her to travel a
distance of