Maksimov was a member of the 96 Otdelnaya Aviaeskadrilya (OIAE - independent squadron). The commanding officer of this unit was Kapitan Aleksandr Korobitzin. In June 1941, the unit was based on Izmail airfield and equipped three Polikarpov I-153s and fourteen Polikarpov I-15bis.

During the Axis attack on Soviet Union in June 1941 Rumanian forces attacked the part of the front that included Izmail.

At 14:00 on 22 June 1941, fourteen I-15bis and three I-153s of 96 OIAE (the entire squadron) scrambled from their airfield at Izmail, alarmed by early warning on incoming enemy aircraft- They attacked eight Romanian I.A.R. 37 biplanes of Escadrila 18 bombardament at 1,000 meters over Izmail, close to the estuary of the Danube in southern Bessarabia, claiming five of them shoot down.
The 96 OIAE commander kapitan Aleksandr Korobitzin and starshiy leitenant Maksimov (whose victim fell into the Danube River) each claimed a destroyed. A third was claimed by mladshiy leitenant Boris Maslov from starshiy leitenant Maksimov’s flight. One shared was claimed by starshiy leitenant Lavrentiy Borisov, deputy commander of 96 OIAE, and leitenant Nikolay Cherkasov. The fifth, finally, was claimed as a shared between leitenant Vasiliy Kuroedov (flight commander), leitenant Leonid Khomutov, leitenant Aleksandr Evstigneyev and leitenant Shota Gogmachadze.
In fact, only one I.A.R. 37 was shot down by Soviet fighters, most probably by mladshiy leitenant Maslov while a second was claimed by the 463rd Anti-Aircraft Battery under starshiy leitenant G. Okhota. Maslov returned to base much later than his colleagues on his last drops of fuel. He had pursued an enemy aircraft way behind the line of the Danube until finishing it off deep inside enemy territory. Upon return, ground crew could count many bullet holes in the airframe of Maslov’s I-15bis.
The Rumanian biplanes, which lost two of their numbers, had been escorted by eight He 112B from Grupul 5 Vânatoare.

On 28 June, Maksimov intercepted Rumanian He112Bs, which attacked Kiliya and Izmail. He shot down two of them. One of the Romanian pilots was killed and the other was wounded but he successfully baled out of his stricken Heinkel and landed on the Romanian side of the front. Escadrila 51 (51 Squadron) of the FARR lost aircraft no. 6 and 8 in this combat. Romanian records claim that no. 8, which was flown by Sublocotenent aviator Constantin Smeu, was hit by anti-aircraft fire while providing long range fighter escort to bombers attacking Kiliya and Izmail Harbours on the left bank of the Danube River. On its way back, the He 112 ran out of fuel and was forced to land 16km from Râmnicul Savat in Moldavia. During the rough wheel-up landing, the central fuel tank exploded and the already wounded pilot suffered burns. He was hurried to a nearby hospital where he died on 2 July. The second Heinkel with no. 6, which was flown by Sublocotenent aviator Constantin Stancu crash-landed and caught fire on Romanian territory following a dogfight with Soviet fighters with the pilot wounded.

He was then transferred to the 26 IAP, which operated on the Leningrad Front.

On the evening of 4 April 1942 more than one hundred aircraft from KG 1, KG 4, StG 2 and JG 54 joined together in a single concentration to attack Soviet ships on the Neva River in Leningrad in a mission code named ”Eisstoss” (Ice Thrust).
VVS-KBF scrambled 3 and 4 GIAPs and 71 IAP, while Leningrad PVO scrambled 26 IAP against the raid. The Soviet fighters were however intercepted by the escorting Bf 109s at a lower altitude and suffered heavily without being able to deal the raiders any losses.
During the drawn-out air combat, JG54 claimed twenty Soviet fighters shot down – including the 2000th victory by JG 54, claimed by Oberfeldwebel Rudolf Klemm (totally 42 victories). One of the shot down and killed pilots was leitenant Maksimov, who was shot down over Seiskari Island in the Gulf of Finland.
The Soviets reported 18 German aircraft shot down, but this is totally unsupported with Luftwaffe loss statistics, according to which not a single German aircraft was lost over Leningrad on this date.
The German raid was however a failure when the Soviet ships only suffered minor damages.

At the time of his death, Maksimov was credited with 3 biplane victories.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1941
1	22/06/41	14:00	1	I.A.R. 37 (a)	Destroyed	I-15bis (b)		Izmail area	96 OIAE
2	28/06/41		1	He112 (c)	Destroyed	I-153		Izmail area	96 OIAE
3	28/06/41		1	He112 (d)	Destroyed	I-153		Izmail area	96 OIAE

Biplane victories: 3 destroyed.
TOTAL: 3 destroyed.
(a) Claimed in combat with I.A.R. 37s from Escadrila 18 bombardament, which lost 2 aircraft (1 to AA fire). 96 OIAE claimed 5 destroyed without losses.
(b) This victory may have been claimed while flying an I-15bis or an I-153.
(c) Probably He 112 no. 8 of Escadrila 51 (51 Squadron) of the FARR flown by Second Lieutenant Constantin Smeu who was killed when he crash-landed.
(d) Probably He 112 no. 6 of Escadrila 51 (51 Squadron) of the FARR flown by Sub Lieutenant Constantin Stancu who was wounded.

Sources:
All aces of Stalin 1936-1953 – Mikhail Bykov, 2014
Black Cross/Red Star Volume II - Christer Bergström and Andrey Mikhailov, 2001 Pacifica Military History, ISBN 0-935553-51-7
From Barbarossa to Odessa: Volume 1 – Dénes Bernád, Dmitriy Karlenko and Jean-Louis Roba, 2007 Ian Allan Publishing Ltd, ISBN 978-85780-273-3
Heinkel He 112 in action - Dénes Bernád, 1996 Squadron/Signal Publications, Carrollton kindly provided by Ondrej Repka
Morskie letchiki v oborone Odessy - A.P. Dorokhov, 1982 Mayak, Odessa, kindly provided by Yuri Shakhov
Rumanian Air Force: The Prime Decade, 1938-1947 - Dénes Bernád, 1999 Squadron/Signal Publications, Carrollton, ISBN 0-89747-402-3
Sovetskaya aviacia nad morem - Sergey Bogatyrev, 1999 Aviacia i Vremya 3/99, Ukraine kindly provided by Ondrej Repka
Vtorzhenye, part III - Dmitriy Khazanov, 1996 Aviacia i Vremya 5/96, Ukraine kindly provided by Ondrej Repka
Additional information kindly provided by Mirek Wawrzynski