o near the bottom.

(3) A combination of deep mines with a patrolling force of surface craft
and aircraft whose object would be to force the submarines under the
surface into the minefield.

(4) A force of surface craft and aircraft patrolling an area of
sufficient extent to prevent submarines coming to the surface to
recharge their batteries during the hours of darkness.

Admiral Mayo was informed that in our opinion the first scheme as given
above, viz. _that of absolutely sealing the exits, was the only radical
cure for the evil_, but that there were very great difficulties to be
overcome before such an operation could be successfully carried out. He
was shown the plan that had been prepared for a mechanical block of all
the enemy North Sea bases, and he entirely concurred in the
impracticability of carrying it out. Such a plan had been advocated by
some officers and by other people; it was, of course, most attractive in
theory and appealed strongly to those who looked at the question
superficially. When, however, a definite operation came to be worked out
in detail the difficulties became very apparent, and even enthusiastic
supporters of the _idea_ were forced to change their views. It was not a
matter for surprise to me that the idea of sealing the exits from
submarine bases was urged by so many people on both sides of the
Atlantic. It was, of course, the obvious counter to the submarine
campaign, and it appealed with force to that considerable section which
feels vaguely, and rightly, that _offensive_ action is needed, without
being quite so clear as to the means by which it is to be carried out.

In this particular case I informed the clever and able officers to whom
the planning of the operation was entrusted that they were to proceed on
the assumption that we intended to seal the enemy's ports somehow, and
that they were to devise the best possible scheme, drawing up all the
necessary orders for the operations. This was done in the most complete
detail and with great care and ingenuity, but at the end there was no
difference of opinion whatever as to the inadvisability of proceeding
with the operations.

It is to be observed in connexion with this question that sealing the
North Sea bases would not have been a complete cure, since submarines
could still make their exit via the Kattegat, where we could not block
channels without violating the neutrality of other nations.

The final conclusion arrived at _