rom submarines when in a submerged
condition. Against this form of attack the gun armament of cruisers or
armed merchant ships was practically useless, and, however powerfully
armed, ships of this type were themselves in peril of being torpedoed.
Small vessels of shallow draught, possessing high speed, offered the
only practicable form of protection. Shallow draught was necessary in
order that the protecting vessels should themselves be comparatively
immune from successful torpedo fire, and speed was essential for
offensive operations against the submarines.

Convoy sailing was, as has been stated, the recognized method of trade
protection in the old wars, and this was a strong argument in favour of
its adoption in the late war. It should, however, be clearly understood
that the conditions had entirely changed. Convoy sailing for the
protection of merchant ships against torpedo attack by submarines was
quite a different matter from such a system as a preventive against
attack by surface vessels and involved far greater difficulties. In the
days of sailing ships especially, accurate station keeping was not very
necessary, and the ships comprising the convoy sailed in loose order and
covered a considerable area of water. On a strange vessel, also a
sailing vessel, being sighted, the protecting frigate or frigates would
proceed to investigate her character, whilst the ships composing the
convoy closed in towards one another or steered a course that would take
them out of danger.

In the circumstances with which we were dealing in 1917 the requirements
were quite otherwise. It was essential for the protection of the convoy
that the ships should keep close and accurate station and should be able
to manoeuvre by signal. Close station was enjoined by the necessity of
reducing the area covered by the convoy; accurate station was required
to ensure safety from collision and freedom of manoeuvre. It will be
realized that a convoy comprising twenty to thirty vessels occupies
considerable space, even when steaming in the usual formation of four,
five or six columns. Since the number of destroyers or sloops that could
be provided for screening the convoy from torpedo attack by submarines
was bound to be very limited under any conditions, it was essential that
the columns of ships should be as short as possible; in other words,
that the ships should follow one another at close intervals, so that the
destroyers on each side of the co