On 1 September 1939 I./ZG 2 was informally named as Jagdgruppe 102 (JGr 102—102nd Fighter Group) and flew the Bf 109D. Production at Messerschmitt plants had not reached expectations and the Bf 110 was not delivered to ZG 2 until 1940.
Bf 109s equipped seven of the ten Zerstörer groups.
I. and II.
Gruppe of Zerstörergeschwader 26 (ZG 26—26th Destroyer Wing) were the only exceptions.
Just 102 Bf 110s were in service on 1 September 1939.
The unit was attached to Sturzkampfgeschwader 77 (StG 77—77th Dive Bomber Wing), a Junkers Ju 87 Stuka unit under the command of Günter Schwartzkopff.
All three staffeln and the Geschwaderstab was operational at Gross-Stein (Stab.,
1 and 3 staffeln) and Zipser-Neudorff (2.
Staffel).
StG 77 and its subordinated Jagdgruppe were placed under the command of Wolfram Freiherr von Richthofen's Fliegerführer zbV which became the Fliegerkorps VIII.
Richthofen's forces operated under the command of Luftflotte 4.
According to German plans, Richthofen's forces were to strike into Lesser Poland, toward Krakow, Łódź and Radom in support of the 10th and 14th Armies.
JGr 102 [I./ZG 2], had 46 Bf 109Ds combat ready.

The German invasion of Poland began on the 1 September 1939.
The invasion began World War II.
The Bf 110 Zerstörergeschwader, Zerstörergeschwader 76 (ZG 76—76th Destroyer Wing) and ZG 26 distinguished themselves in the fighter escort role as the long-range bomber pilots from Kampfgeschwader 27 attacked Warsaw airfields to destroy the Polish Air Force.
JGr 102, under the command of Hauptmann Gentzen claimed 28 Polish aircraft in aerial combat and a further 50 on the ground.
Colonel Stefan Pawlikowski's Warsaw Pursuit Brigade resisted fiercely but lost 17 percent of its fighting strength on 1 September which rose to 72 over the next five days.
The unit may have claimed as many as 29 in the air and 78 on the ground.
One of JGr 102's missions was providing fighter escort for Ju 87 Stuka dive-bombers in the Bombing of Wieluń.
No Polish aerial resistance was encountered.
Gentzen claimed seven victories in two days: on 3 September he shot down a PZL.37 Łoś medium bomber and two PZL P.11 fighters.
The next day he claimed four PZL.23 Karaś attack-bombers.
On the 3rd, the Polish Air Force flew 90 sorties in the Częstochowa-Radomsko area as bombing intensified.
The Poles did lose nine P.23s in the area as JGr 102 [I./ZG 2] and I./JG 76 were unleashed on combat patrols.

During the Battle of Łódź, the Łódź Army was left without a fighter shield which had been destroyed by Zerstörer groups days earlier.
Gentzen's Bf 109 group completed its destruction by claiming five of its number on 2 September 1939.
JGr 102's parent unit, StG 77 continued to support the invasion, and fought in the Battle of Radom and the Siege of Warsaw.
Johannes Gentzen, the commanding officer, remarked that the Bf 109 pilot's success over Poland depended largely on luck.
Gentzen remarked the Polish were masters of camouflage, the olive-brown combination blended excellently with the landscape.
On one occasion, he managed to shoot down a Polish fighter, which glided and landed on a heavily camouflaged airfield before it burst into flames while the pilot ran for cover.
The German pilots would not have noticed its existence but for the aerial combat.
According to Glentzen, the group proceeded to strafe the airfield, knocking out five Polish bombers and then firing at a row of haystacks which masked more fighter aircraft.
JGr 102 based itself at Krakow airfield during the northward advance.
Gentzen proved to be the sole Bf 109 flying ace over Poland.
The action occurred at Widzew, east of Lodz.
The Polish 161 Eskadra lost five fighters.
The group continued to fly three to four sorties per day.
Based at Debrica on 13 September, a erman reconnaissance aircraft delivered a message notifying the unit that an airfield at Brody was full of aircraft.
For one Bf 109D, they claimed seven PZL.37 Łoś while Gentzen claimed four two-seater aircraft which were flying nearby, apparently without gunners.
Over Brody, in 48 hours, the group claimed 26 Polish
On 1 September 1939 I./ZG 2 was informally named as Jagdgruppe 102 (JGr 102—102nd Fighter Group) and flew the Bf 109D. Production at Messerschmitt plants had not reached expectations and the Bf 110 was not delivered to ZG 2 until 1940. Bf 109s equipped seven of the ten Zerstörer groups. I. and II. Gruppe of Zerstörergeschwader 26 (ZG 26—26th Destroyer Wing) were the only exceptions. Just 102 Bf 110s were in service on 1 September 1939. The unit was attached to Sturzkampfgeschwader 77 (StG 77—77th Dive Bomber Wing), a Junkers Ju 87 Stuka unit under the command of Günter Schwartzkopff. All three staffeln and the Geschwaderstab was operational at Gross-Stein (Stab., 1 and 3 staffeln) and Zipser-Neudorff (2. Staffel). StG 77 and its subordinated Jagdgruppe were placed under the command of Wolfram Freiherr von Richthofen's Fliegerführer zbV which became the Fliegerkorps VIII. Richthofen's forces operated under the command of Luftflotte 4. According to German plans, Richthofen's forces were to strike into Lesser Poland, toward Krakow, Łódź and Radom in support of the 10th and 14th Armies. JGr 102 [I./ZG 2], had 46 Bf 109Ds combat ready.
The German invasion of Poland began on the 1 September 1939. The invasion began World War II. The Bf 110 Zerstörergeschwader, Zerstörergeschwader 76 (ZG 76—76th Destroyer Wing) and ZG 26 distinguished themselves in the fighter escort role as the long-range bomber pilots from Kampfgeschwader 27 attacked Warsaw airfields to destroy the Polish Air Force. JGr 102, under the command of Hauptmann Gentzen claimed 28 Polish aircraft in aerial combat and a further 50 on the ground. Colonel Stefan Pawlikowski's Warsaw Pursuit Brigade resisted fiercely but lost 17 percent of its fighting strength on 1 September which rose to 72 over the next five days. The unit may have claimed as many as 29 in the air and 78 on the ground. One of JGr 102's missions was providing fighter escort for Ju 87 Stuka dive-bombers in the Bombing of Wieluń. No Polish aerial resistance was encountered. Gentzen claimed seven victories in two days: on 3 September he shot down a PZL.37 Łoś medium bomber and two PZL P.11 fighters. The next day he claimed four PZL.23 Karaś attack-bombers. On the 3rd, the Polish Air Force flew 90 sorties in the Częstochowa-Radomsko area as bombing intensified. The Poles did lose nine P.23s in the area as JGr 102 [I./ZG 2] and I./JG 76 were unleashed on combat patrols.
During the Battle of Łódź, the Łódź Army was left without a fighter shield which had been destroyed by Zerstörer groups days earlier. Gentzen's Bf 109 group completed its destruction by claiming five of its number on 2 September 1939. JGr 102's parent unit, StG 77 continued to support the invasion, and fought in the Battle of Radom and the Siege of Warsaw. Johannes Gentzen, the commanding officer, remarked that the Bf 109 pilot's success over Poland depended largely on luck. Gentzen remarked the Polish were masters of camouflage, the olive-brown combination blended excellently with the landscape. On one occasion, he managed to shoot down a Polish fighter, which glided and landed on a heavily camouflaged airfield before it burst into flames while the pilot ran for cover. The German pilots would not have noticed its existence but for the aerial combat. According to Glentzen, the group proceeded to strafe the airfield, knocking out five Polish bombers and then firing at a row of haystacks which masked more fighter aircraft. JGr 102 based itself at Krakow airfield during the northward advance. Gentzen proved to be the sole Bf 109 flying ace over Poland. The action occurred at Widzew, east of Lodz. The Polish 161 Eskadra lost five fighters. The group continued to fly three to four sorties per day. Based at Debrica on 13 September, a erman reconnaissance aircraft delivered a message notifying the unit that an airfield at Brody was full of aircraft. For one Bf 109D, they claimed seven PZL.37 Łoś while Gentzen claimed four two-seater aircraft which were flying nearby, apparently without gunners. Over Brody, in 48 hours, the group claimed 26 Polish 
Zerstörergeschwader 2