ss. The most vulnerable part
of the East Coast, from the Forth to the Thames, or from North Berwick
to Clacton, was to be patrolled by the Naval Air Service. But these
arrangements were soon altered. Not many days after the outbreak of war
the Germans established themselves in Belgium, and it was believed that
they would use Belgium as a base for formidable attacks by aircraft on
the Thames estuary and London. The forces of the Naval Air Service were
therefore concentrated between the Humber and the Thames, from Immingham
to Clacton. The Wash was thought to be the most likely landfall for a
German airship raiding London. Regular patrols of the coast were carried
out in the early days of the war, to report the movements of all enemy
ships and aircraft and to detect enemy submarines. But there was not
much to report, and it was weary work waiting for the enemy to begin.

The British Expeditionary Force was ready for service abroad, and it
fell to the Naval Air Service to watch over its passage across the
Channel. A regular patrol between Westgate, close to the North Foreland,
and Ostend was maintained by seaplanes, following one another at
intervals of two hours. On the 13th of August a temporary seaplane base
was established at Ostend under the command of Flight Lieutenant E. T.
R. Chambers, but on the 22nd of August, when the expeditionary force was
safely landed and the occupation of Ostend by the Germans seemed
imminent, the base was withdrawn, and the men and stores were taken back
to England. An airship patrol of the Channel undertaken by airships Nos.
3 and 4 (that is to say, by the _Astra-Torres_ and _Parseval_) began on
the 10th of August, and was continued throughout the month. The average
time of flight of a seaplane on patrol was about three hours, of an
airship about twelve hours, so that the airship, which could slacken its
speed and hover, had the advantage in observation. The chart printed on
p. 363 illustrates the patrols carried out by the two airships on the
13th of August 1914. Here are copies of their logs for the day:

'_Log of No. 3 Airship, 13th August 1914._

7.10 a.m. Rose.
7.37 Passed Sittingbourne.
7.45 Passed Teynham Station.
7.50 Passed Faversham.
8.20 Passed Canterbury.
9.0 Passed Coastguard Station.
9.49 Sighted No. 4 Airship.
10.41 Sighted seaplane on starboard quarter.
5.50 p.m. Altered course for Coastguard Station.
6.25