Weather: showery.
The German attack against coastal shipping had started at the beginning of July. However, the official date of the beginning of the Battle was fixed on July 10th. The first German aircraft picked up by radar were reconnaissance planes looking for convoys which could be attacked. There were also the long range aircraft whose job was to fly deep into the Atlantic ascertaining what kind of weather could be expected over Britain in a day or so. The action began in the morning with an attack on a convoy and a sharp attack on Swansea which resulted in some 30 civilian deaths. This was followed by serious action in the afternoon. Around 1.30pm the tell-tale blips indicating a large concentration of Luftwaffe aircraft had begun to appear on the cathode ray tubes of the receiving sets in the radar scanning huts in which WAAFs were on the lookout for exactly this kind of warning. What they indicated was a flight of some 26 Dornier 17 bombers accompanied by 26 Me109 fighters plus 40 Me110s.
The convoy was being patrolled by half a dozen Hurricanes. The latter were soon to be joined by elements of 4 squadrons from 11 Group. In the fight which followed the Luftwaffe lost 4 planes shot down. The RAF lost 3 Hurricanes, one of which collided with a German bomber losing half its wing and crashing into the sea. The damage was one coastal ship sunk.
The tally for the day was 13 Luftwaffe aircraft shot down at the cost of 7 RAF fighters lost. The RAF had flown 609 sorties in the day and had managed to achieve a two to one victory over the enemy. Not bad in its first encounter with its much more experienced adversary. A particular feature of the day was the relatively indifferent performance of the twin-engine fighter, the Me110. These aircraft had been forced to fly in a tight circle to defend themselves, relying on their rear gunners. But it also became clear that the RAF was going to be outnumbered in the Battle to follow. They were only going to be able to intercept many of the raids of the Luftwaffe by flying a large number of sorties each day.
54 Squadron Operational Record Book, 10 July 
As a result of the first phase of the Battle for Britain, the squadron could only muster 8 aircraft and 13 pilots.
242 Squadron Operational Record Book, 10 July
Convoy patrol over sea. First enemy bomber shot down by Squadron in this section. Shot down by Sub-Lt Gardner. 2 others damaged.