The Battle of Britain officially began on Wednesday 10 July

A Boulton-Paul Defiant of No. 264 squadron. The heavy rear turret meant that the fighter could not carry forward-facing armament, as its performance was severely affected.

Two day fighter squadrons, Nos 141 and 264, were equipped with the Defiant during the battle of Britain. Its sole armament comprised four .303in machine guns in a power-operated turret. The two squadrons suffered high losses in the battle. 

The Battle of Britain officially began on Wednesday 10 July, though with only two losses to enemy action (and with four aircraft being damaged), it was a quieter day for Fighter Command than many of those that had gone before. With nine enemy aircraft shot down (and with five more severely damaged in combat) it was also a more successful day than some. This was perhaps just as well, since some units were already beginning to show signs of strain. No.54 Squadron, for example, had been reduced to eight aircraft (from 12) and 13 pilots (from 18), while No.79 Squadron's pilots were in such a poor state that they were ordered north for a rest. Historian Francis Mason said of them that they had 'reached the stage of physical and mental exhaustion at which they were of minimal value to the defence, and represented a distinct danger to themselves.' Unfortunately, No.79 Squadron's place in the frontline was taken by the Defiants of No.141 Squadron, which were not destined to be any more successful.

The 10 July broke with thick cloud and thundery rain, and with eight convoys at sea in British coastal waters. The largest of these was 'Bread', which set off from the Thames Estuary with the morning tide, rounding the North Foreland soon after 1000. About three quarters of an hour later, six No.74 Squadron Spitfires intercepted a solitary reconnaissance Do 17P - and its escort of an entire Gruppe of JG 51 Bf 109Es. The escorts did their job well, and prevented all but a couple of attacks. The Dornier limped home (with dead and wounded crew), and two of the Spitfires had to force land at Manston. A covering Free Chase over Kent drew up N0.610 Squadron, one of whose Spitfires was shot down.

With the return of the reconnaissance Do 17, the Luftwaffe began planning a major attack, and although six No.32 Squadron Hurricanes were over the convoy as the raid struck, they required reinforcement. As a result, the 26 Do 172s of I./KG 2, and the escort of five Staffeln of Bf 110s and Bf 109s, were met by seven Hurricanes from No.56 Squadron, nine from No.111, and by eight No.74 Squadron Spitfires, as well as the six original Hurricanes. With some 60 enemy fighters and 30 RAF fighters, the odds were more even than was often the case, and a massive melee developed. This opened with a head-on attack against the enemy formation by Nos 32 and 111 Squadrons in line-abreast, which distracted the enemy bomb aimers sufficiently to ensure that only one hit was scored of 150 bombs dropped. German morale was not dented, however, and when they returned to base, the jubilant bomb-aimers claimed four merchant ships sunk, plus a heavy cruiser, together with 11 of the attacking RAF fighters! Before the fight was over, six No.64 Squadron Spitfires joined the fray, and these harassed the retreating Bf 110s back to the French coast, severely damaging one. The other RAF fighters involved in the action downed three and damaged several enemy aircraft without loss to themselves, bringing the day's score to nine enemy aircraft destroyed.

A mass raid by 63 Luftflotte 3 Ju 88s against Falmouth and Swansea escaped interception but fortunately did little damage. No.92 Squadron at Pembrey were scrambled too late to intercept. The raid was, however, intercepted by Wing Commander Ira Jones, a First World War veteran serving as Wing Commander (Flying) at Stormy Down. He took off in an unarmed Hawker Henley and loosed off his Verey signal pistol at a Ju 88 'with considerably more feeling than effect.'

The 10 July ended with about 20 enemy bombers roaming over southern England, aiming at any 'chinks' in the blackout. This was pointless and unproductive, and served no real purpose other than to stoke up anti-German feeling in Britain. Hitler had yet to issue his final 'appeal to reason', and may not have realised that Britain's civilian population was being targeted.