A good deal of reconnaissance was carried on by the squadrons during the northward move of the army. On the 29th of September unusual and heavy movement in a northerly and north-westerly direction had been observed behind the enemy lines on the Aisne. On the 1st of October air reconnaissances showed that the trenches in front of the British First Army Corps were unoccupied or very lightly held, and during the next few days there were many indications that one or two German army corps were being withdrawn to the north. Meantime the enemy took more trouble than usual to interfere with our aircraft, and employed an increased number of anti-aircraft guns. In the north our strategic reconnaissances were not so successful, and the formidable enemy movement against the Ypres line developed undetected. Not many aeroplanes were available at this time for the wider sort of strategic reconnaissance. Nos. 2, 3, and 5 Squadrons had been attached, by an order issued on the 1st of October, to the First, Second, and Third Army Corps respectively, while No. 4 Squadron was detailed for strategical reconnaissance. The General Officers Commanding army corps had learned the value of aeroplanes and demanded their assistance. Much of the country over which they were operating in Northern France and Flanders was flat and enclosed, unsuitable either way for cavalry reconnaissance. Long-distance work was done chiefly from headquarters. On the 3rd of October, when the situation at Antwerp had become critical, Lieutenant-Colonel F. H. Sykes flew direct to Bruges from Fere-en-Tardenois, with a message from Sir John French to the Belgian Chief of Staff at Antwerp. On the following day he returned and reported that the Germans had broken through the south-eastern sector of the outer defences of Antwerp, that the Belgians were awaiting help, and that they might possibly hold out for two or three weeks. In forwarding the report to Lord Kitchener Sir John French adds, 'The relief of Antwerp I regard as my first objective'. This mission was followed by others, and a few days later Sir John French speaks of reports which he is receiving daily by air from General Rawlinson.