[6] On 1 September 1939 Adolf Hitler issued orders for Fall Weiss (Case White) to be implemented and the Wehrmacht attacked Poland.

[7] Commander-in-chief of Luftflotte 4, Alexander Löhr, ordered KG 55 into action and the wing bombed railway targets in support of the German Fourth Army.

III./KG 55 was confined to more northern operations: attacking Verdun on 16 May and flying the only known mission of the unit in the Battle of Belgium, to Charleroi, three days earlier on 13 May before moving to Eutingen on 24 May.

On 12 May Allied fighters shot down a Heinkel of 4./KG 55, whilst it was attacking railway targets North East of Reims, for the unit's first loss of the battle.

[20] Between 20 and 23 June 1940, KG 55 were already operating over the United Kingdom, bombing targets in Bristol and Cardiff flying from forward airfields near Paris.

On 26 August it took part in Luftflotte 3's last major daylight raid for three weeks as the air fleet was reassigned to attacking the West and East Midlands industrial areas.

Four Erprobungsgruppe 210s Bf 110s were shot down, but the Heinkels were protected as KG 55 escaped without loss but was forced to abandon the mission, drop its bombs and retreat to France.

The Blitz, as it became known, was a series of heavy attacks against British cities in order to break the will of the civil population and destroy its industrial centres.

The crews were highly experienced in night operations and selected to help lead the attacks under the command of Major Friedrich Kless.

The three units operated in unison often: KGr 100 illuminated the target with incendiaries and the later formations dropped high explosive bombs to destroy water mains and impede fire-fighting efforts.

They also learned to navigate by using searchlights and shell bursts from anti-aircraft artillery as a reference point because they denoted the close proximity of cities, coastlines and lights were often connected to railways.

In one incident the British jamming succeeded in confusing the KG 55 He 111 piloted by Leutnant Hans Thurner, who landed on three occasions on RAF airfields in rapid succession before realising his error and escaping across the Channel.

[57] The attack is notable as 5 staffel of II./KG 55 lost two He 111s to night fighters this night—Pilot Feldwebel Karl Brüning became a prisoner of war but his crew were killed by a Boulton Paul Defiant from No.

[1] The last attacks were flown against Hull, Southampton, Avonmouth, London, Bristol, Clydeside and Devonport from 16 to 22 April; casualties amounted to two badly damaged Heinkels.

[60] KG 55's units began a last minute withdrawal to the Eastern borders of the Reich in preparation for Operation Barbarossa, the war on the Soviet Union.

KG 55 was to provide air support for Army Group South attacking into Ukraine in its drive toward the Caucasus and the Soviet oil fields.

[65] On 26 June 1941 KG 55 was involved in the battles to support the 1st Panzer Army, operating against land-air forces belonging to the Soviet Western Front.

Lacking dive-bomber, or strike aircraft, the air corps was forced to employ its medium bombers in the close support role.

On 26 June an attack hit the headquarters of the Soviet 15th Mechanised Corps, wounding commander Major General Ignat Karpezo.

"[65] Despite the losses, on 1 July, the three Geschwadern thwarted the Soviet retreat to Kiev, routing the infantry columns disengaging from the German 16th and 17th Armies.

The dusty and ill-prepared roads were ill-suited to transporting large amounts of equipment and the Red Army relied on rail systems for logistics.

From the 8–15 May, it was directed to support Erich von Manstein's army group in the Crimea, Operation Trappenjagd (Bustard-Hunt): attacks on Dzhankoi, Bagerovo, Kerch and the Sea of Azov were carried out on 10 May.

[66] The group damaged the minesweeper Komintern and sank a transport ship on 21 April and by this time the Black Sea Fleets ability to supply the Soviet forces in Sevastopol was severely curtailed.

II./KG 55 attacked Red Army columns along the Marayevka-Kerch road on 10 May and five days later it had been withdrawn to support German forces in the Izyum-Kupyansk region.

It briefly flew night reconnaissance missions over northeastern Italy, searching possible invasion routes for Operation Achse, in the event the Italians left the Axis powers.

[97] During repeated attacks between 4 and 22 June, all of the plant's 50 buildings, 9,000 metres of conveyors, 5,900 units of process equipment and 8,000 engines were destroyed or damaged.

[84] II./KG 55 flew two missions on the 9 July and lost at least one bomber and one damaged in combat with Soviet fighters and after being engaged by strong anti-aircraft fire.

[3] The German defeat in the Crimea on 12 May, necessitated aircraft to evacuate personnel and KG 55 was called in to do so from 11 to 15 May, operating from Focsani, Romania.It transferred to Dęblin on 16 May, but had 35 He 111 H-16s on strength on 1 June 1944.

[5] It withdrew to Germany to carry out air-supply flights to German Garrisons in isolated French ports from 10 to 12 September after Operation Overlord and Battle for Normandy, and liberated the bulk of France and Belgium over June–September 1944.

It appears some of the unit personnel were in action earlier, as on 28 May an entry was made for the squadron's first loss on a bombing operation against Krapotkin train station in the northern Caucasus.