Bristol Blenheim, part eleven. The Blenheim during the Battle of Britain and early Mediterranean campaign.

 

The Bristol Blenheim was armed with a single forward-firing 0.303 in (7.7 mm) Browning machine gun outboard of port engine with a 0.303 in Lewis machine gun placed in a dorsal turret firing to the rear. After the Campaign of France, the Lewis was replaced by a more modern 0.303 in Vickers VGO machine gun. A total amount 1.000 lb (450 kg) of bombs could be carried in the internal bomb bay located at the central part of the fuselage. Like most contemporary British bomber aircraft of the time, bomb bay doors were closed with bungee cords and opened with the weight of the released bombs. As there was no way to predict how long would it take for the bombs to open the doors, bombing accuracy was low. The bomb bay could also be loaded with a hand-operated winch which was part of the fuselage. 

Blenheim-equipped squadrons operated throughout the Battle of Britain, suffering heavy losses, although they never received the publicity that fighter squadrons had. From July to December 1940 Blenheims often raided German airfields in France during both day and night. Most of those raids were unproductive though. However, there were some successes. On 1st August twelve Blenheims were sent to attack the airfields in Haamstede (Netherlands) and Evere (Brussels - Belgium) where they destroyed or heavily damaged three Messerschmitt Bf.109 of II./JG.27 and killing a German ace. Two additional Bf.109 were claimed by Blenheim gunners. On 7th August another successful raid was carried on by a single Blenheim which destroyed one Bf.109 of 4./JG.54, heavily damaged another one and caused light damage to four more fighters.

Some other missions however, were not that successful and had an almost 100% of loss rate among the Blenheims. One of those operations was a raid carried out on 13th August 1940 against a Luftwaffe airfield in Aalborg, Denmark by twelve Blenheims of the No 82 Squadron. On their way to the target, one Blenheim returned early (for this, the pilot was charged, but he was killed later during a mission before a martial court was held), the remaining eleven reached Denmark but were shot down. Five by flak and six by Bf.109s. The Blenheim was also used to carry out reconnaissance missions over Germany and German-occupied lands. In this role, the Blenheim proved to be, again, too vulnerable and slow against Luftwaffe fighters and their casualty rate was high. 

From 5th September 1940 Blenheims began to target German-occupied ports along the English channel, together with heavier bomber types. They also performed anti-shipping patrols, as Coastal Command's strike squadrons were heavily depleted through the second half of 1940. On 11th March 1940 a Blenheim registered as P4852 became the first Royal Air Force's aircraft to sink an u-boat scoring two direct hits on U-31 at Schillig Roads. 

The Blenheim was also extensively employed in the Mediterranean theatre. When Italy declared war in June 1940, there were five Blenheim squadrons stationed in Egypt, three at Aden and one in Iraq. Bombing raids against Italian positions were almost immediate in North Africa, however, operations there and in East Africa were sporadic until late 1940.

During Operation Compass in December 1940 both Blenheim and Wellington squadrons were active during the whole operation bombing both enemy encampments and important strongholds such as Tobruk and Benghazi. Four Blenheim units, squadrons No 11, 30 and 84 and 113 (which was sent to Greece in October 1940) were reinforced by No 211 squadron in March 1941 (which came from Greece). The squadrons operated under extremely primitive conditions and couldn't mount an effective bombing campaign. 

Sources:

1.  https://en.wikipedia.org/wiki/Bristol_Blenheim

2. Signal Squadron - Aircraft In action 88 - Bristol Blenheim in Action

3. Hall Park Books - Warpaint 26 - Bristol Blenheim

4.Osprey Publishing - Combat Aircraft 5 - Blenheim Squadrons of World War 2