greatest secrecy for the whole
operation.

The next matter for trial was the arrangement devised by Sir R. Bacon
for making it possible for tanks to mount the sea wall. These trials
were carried out with great secrecy against a model of the sea wall
built at the Headquarters of the Tank Corps in France, and were quite
successful. It was necessary to see actual photographs of the tanks
mounting the coping at the top of the sea wall to be convinced of the
practicability of the scheme. A matter of great importance was the
necessity for obtaining accurate information of the slope of the beach
at the projected landing places in order that the practicability of
grounding the pontoon could be ascertained. This information Sir R.
Bacon, with his characteristic patience and ingenuity, obtained by means
of aerial photographs taken at various states of tide.

Finally, to gain exact knowledge of the rise and fall of the tide,
Admiral Bacon employed a submarine which submerged in the vicinity of
Nieuport and registered the height of water above her hull for a period
of twenty-four hours under conditions of spring and neap tides.

The preparations for the landing involved much collaboration with the
military authorities, and Sir Reginald Bacon was frequently at G.H.Q.
for the purpose. As soon as it was decided that the 1st Division was to
provide the landing party, conferences took place between Admiral Bacon
and General Sir Henry Rawlinson (now Lord Rawlinson), and I took the
opportunity of a visit paid by Sir H. Rawlinson to London to confer with
him myself. Subsequently a conference took place at the War Office at
which Sir Douglas Haig was present.

There was entire unanimity between the Navy and Army over the proposed
operation, and we greatly admired the manner in which the Sister Service
took up the work of preparing for the landing. Secrecy was absolutely
vital to success, as the whole scheme was dependent on the operation
being a surprise, more particularly in the selection of the landing
place. Admiral Bacon describes in his book the methods by which secrecy
was preserved. As time passed, and the atrocious weather in Flanders
during the summer of 1917 prevented the advance of our Army, it became
more and more difficult to preserve secrecy; but although the fact that
some operation of the kind was in preparation gradually became known to
an increasing number of people, it is safe to say that the enemy never
realized unti