In December 1939, mladshiy leytenant Filatov served in 25 IAP, which took part in the Finnish-Soviet Winter War equipped with Polikarpov I-16s.

At 11:30 on 19 December, leytenant Viktor Vilchik and mladshiy leytenant Filatov claimed one Fokker D.XXIs each over Kämära, 5 kilometres east of Viipuri.
Totally, 25 IAP claimed four Fokker D.XXIs during the day; the two other were claimed by kapitan N I. Zhuralev’s I-16 flight. It is possible that these were claimed in combat with Fokkers from LLv 24 and LLv 26, which reported combat against SBs and DB-3s during the day. LLv 24 flew 58 sorties on the Karelian Isthmus and was engaged in combat on 22 occasions between 10:50 and 15:20. The VVS lost 16 SBs, including five from 13 SBAP and eight from 44 SBAP, and one DB-3 from 1./6 DBAP. Ylikersantti Kelpo Virta (FR-84) was first in action and claimed one and one probable I-16s (possibly from 68 IAP) over Muolaanjärvi between 10:15-10:25, both crashes witnessed by ground troops but it seems that actually only one fighter pilot from 4./49 IAP was lost on this date. Luutnantti Per-Erik Sovelius (FR-92) of LLv 24 reported:

“On 19.12.39 from 0955 to 1105 on air combat patrol. I was leading the 3rd pair with kersantti Ikonen on my wing. We took off by the announcement. I flew over Antrea area when the radio informed 45 and I headed towars south-west. Somewhere near Kämärä, I observed a 7-plane SB formation and started the chase. The SBs were flying toward southwest, but turned towards south. However, we did not gain them, but we observed a bit aside three SB planes flying roughly in the same direction.
Kersantti Ikonen got well behind the plane on the starboard wing and shot it into flames from a very close range at the altitude of 2000 metres over Kipinola. I tried to get behind the port wingman, but did not have enough speed. I observed another three SB planes heading south-west, tried after them but began to loose them. The planes were throwing leaflets.
During the chase I observed again three SB planes a little below going southwards. I picked the port wingman as my target and shot first to the rear fuselage, when the dorsal gunner quitted firing. After this I aimed the fire to the port engine, which began to smke and finally caught fire. The plane fell to the starboard wing and dived towards the sea close to Seivästö about 10 kilometres from the coast.
I fired then at the starboard wingman, when its right engine started to pour smoke, but it stayed with the lead plane and kept going on.
I did the return flight at 3000 metres and while about 5 kilometres above the land I observed a-a artillery explosions. On the south coast of lake Muolaanjärvi two I-16s managed to take me by surprise coming from the sun. I woke up when bullets rustled in my plane.
I pulled instantly towards them, but noticed soon that the I-16 was more manoeuvrable than the Fokker. I tried to tighten my turns, but got only once the enemy into my sight and fired a short burst. I noticed at the same time that I had ammunition left only in one gun. Once after trying to turn as tight as possible I lost the control and slipped into a spin. I continued to make all sorts of evasive action and down at the surface I managed to shake my pursuers. I was then nearby Heinjoki.
Both I-16s attacked simultaneously and obviously in order to avoid collision did not get straight behind me and were forced to shoot with a small deflection. Judged by the tracers the I-16s seemed to fire all the time even when my plane was clearly out of their sights.
After the mission my plane had two hits. One in the tail plane and the other had gone in through the mg compression bottle hatch and out from the fuselage bottom.”

149 IAP was formed on 31 January 1940 at Pushkin based on elements from 38 IAP and was attached to VVS SZFr. Reinforcements was received from 25 IAP (16 I-16s for 1st Eskadrilya), from 51 IAP (14 I-153s for 2nd eskadrilya arrived on 14 February 1940 from Leningrad) and from the Air Force Academy (VVA) in Moscow.
It seems that leytenant Viktor Vilchik and mladshiy leytenant Filatov were among the pilots transferred from 25 IAP.

On 1 February, 149 IAP moved to Vejno west of Lake Peipus (Chudskoye ozero).

At 10:50 on 20 February, luutnantti Paavo Berg (GL-280) of LLv 26 attacked a detachment of 30 bombers above Kouvola. He attacked a bomber in the middle of the formation but this was a mistake, as he ended up in the middle of murderous crossfire from the bomber formation. His Gladiator caught fire and Berg opened the canopy and unstrapped himself to jump. He, however, got stuck when his boot got jammed in the cockpit and he struggled for a few moments, trying to remove his stuck boot and the flames burnt his face before he fell free from his blazing Gladiator. Later Berg heard that the SB he had attacked dived burning into ground. He was hospitalised for the rest of the winter war.
It seems that the bomber shot down by was SB c/n 7/216 of 5./54 SBAP, which was shot down in air combat over Kouvola and crashed at Kattilainen, Ruokolampi. Leytenant Yevgenij Mikhailovich Filonenko was KIA and mladshiy leytenant Vasiliy Yefimovich Kufakov was killed at arrest. Shturman leytenant Mikhail Ivanovich Maksimov was believed to have been taken prisoner after the forced landing on the ice of Gulf of Finland and on 17 July 1940, the Soviet Legation inquired whether Maksimov had been taken prisoner; in fact, he died of wounds on 21 February.
On the same day alikersantti Ilmari Joensuu (LLv 26) shot down a DB-3 over Laatokka (possibly from 54 SBAP).
During the day six SBs and one DB-3 were lost for various reasons.
149 IAP reported that six I-16s and eleven I-153s were escorting 36 SB-bombers to target no. 32 (Kouvola Junction). Finnish fighters intercepted on the return flight south of Utti and mladshiy leytenant Filatov (I-153) claimed one Fokker and got one hit on his own aircraft. No Finnish Fokkers were lost on this date.

Filatov ended the war with 1 biplane victory and a total of 2.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1939
1	19/12/39	11:30	1	Fokker D.XXI (a)	Destroyed	I-16		Kämärä; 5km E Viipuri	25 IAP
	1940
2	20/02/40		1	Fokker D.XXI (b)	Destroyed	I-153		Utti	149 IAP

Biplane victories: 1 destroyed.
TOTAL: 2 destroyed.
(a) Possibly claimed in combat with Fokker D.XXIs from LLv 24 and 26 which suffered two damaged fighters for claims of four by 25 IAP.
(b) Can’t be verified with Finnish records.

Sources:
All aces of Stalin 1936-1953 – Mikhail Bykov, 2014
Ilmavoitot, osa 1 - Kalevi Keskinen and Kari Stenman, ISBN 952-99432-8-8
Ilmavoitot, osa 2 - Kalevi Keskinen and Kari Stenman, ISBN 952-99432-8-8
Red Stars 7 - Talvisota Ilmassa - The Winter War In the Air - Carl-Fredrik Geust, 2011 Apali Oy, Tampere, ISBN 978-952-5877-04-5
Soviet Aces 1936-1953
Soviet Fighter Pilots 1936-1953 - Mikhail Bykov
Suomen Ilmavoimat part II – 1928-40 – Kalevi Keskinen and Kari Stenman, 2006, ISBN 952-99743-0-2