When Italy invaded Greece on 28 October 1940 Sminagos (Captain) Kellas was in charge of 21 Mira (Squadron) with 12 PZL P.24s based at Kalambaka in the middle of Greece.

On 20 November 1940, Greek PZL P.24 planes of 21 Mira meet Italian bombers with Fiat fighters as escort over Lake Mikri Prespa. During the ensuing dogfight Kellas shot down an Italian Z.1007bis when it tried to escape.

In late 1940 the unit was re-equipped with ex-RAF Gladiators.

In the middle of January 1941 the winter hit Greece with full force paralysing movements and operations. One of the worst hit airfields was Kalambaka in Central Greece, where the Gladiators of 21 Mira were based. When ordered to fly down to Eleusis to cover an incoming convoy, the base personnel were defeated by the task of trying to clear the runway. Sminagos Kellas, the commanding officer, made a plea for help to the local villagers, and about 200 old men, women and children turned up, equipped with a variety of agricultural implements. Working with a will, they cleared the ground sufficiently to allow the squadron to get off the next day.

At noon on 25 January seven 21 Mira Gladiators along with seven PZL P-24s from 22 Mira made a sweep over the Premeti - Kelsyre area. Participating from the 21 Mira were Sminagos Kellas, Sminagos Michail Stilianopoulos, Yposminagos Ioanis Katsaros, Anthiposminagos Anastasios Bardivilias, Episminias Nikolaos Kostorizos, Episminias Nikolaos Stasinopoulos and Episminias Konstantinos Chrizopoulos.
During the patrol they encountered BR.20 bombers from the 116^a Gruppo, 37^o Stormo B.T. The commander of 22 Mira, Sminagos Andreas Antoniou, claimed one shot down (his second during the day after having claimed a Z.1007bis over Salonika in the morning). Another BR.20 was claimed between Kelsyre and Berat by Episminias Panagiotis Argyropoulos of 22 Mira (Antoniou and Argyropoulos later became the Greek Air Force’s only aces). One bomber was attacked by Kellas, who hit its right engine. The BR.20 was heavily damaged and it was then attacked from both the right and left side, by another Gladiator and a PZL, which finished it off.
Kellas also made a head-on attack on three more bombers, but without obvious result.
The Greek claims are confirmed with the Greek Army.
The Italians report one heavily damaged bomber, which forced-landed at Lecce with 3 crew members dead and it seems that one additional bomber made a force-landing near Berat, severely damaged. The gunners in return claimed one PZL.

On 9 February 1941 18 S.79s from the 104^o Gruppo were out to bomb in the Kelcyre-Tepelene area. These bombers were escorted by twelve Fiat G.50bis fighters from the 24^o Gruppo led by Maggiore Eugenio Leotta, and twelve Fiat CR.42s from the 160^o Gruppo, led by Tenente Edoardo Crainz. Four Greek Gladiators of 21 Mira (Sminagos Kellas (CO of 21 Mira), Anthiposminagos Anastasios Bardivilias, Episminias Ilias Dimitrakopoulos and Episminias Nikolaos Kostorizos) and eight PZLs from 22 and 23 Mire intercepted the formation.
The Greek fighters didn’t manage to penetrate the fighter screen and a series of hectic dogfights started with the Italian escort. Overclaiming was heavy on both sides and the Greek pilots claimed eight enemy fighters, Kellas claimed two while Bardivilias, Dimitrakopoulos and Kostorizos claimed one enemy aircraft each. Episminas Epaminondas Dagoulas of 22 Mira claimed one fighter while Yposminagos Marinos Mitralexes from the same unit claimed one fighter over Berat; Mitralexes also claimed one additional fighter and a probable during the combat. The Greek Army confirmed the eight victories and this was also confirmed by a Mr. Roussos, a journalist of the newspaper ELEYTHERON BHMA, who was on the ground with the troops as a war correspondent. His report is a first hand account and also gives the enthusiasm of the Greek soldiers while the Italian planes fell to the ground.
The Gladiators flown by Kellas and Dimitrakopoulos were both hard hit during the combat but it was possible to repair these fighters. Yposminagos Kotronis was shot down, but he managed to force-land his PZL, totally destroying it in the process. He escaped, however, only lightly wounded. A second PZL was shot up by three fighters and Episminias (Sergeant) John Michopoulos of 22 Mira was wounded in the thigh, but he managed to get back to Salonika/Sedes and land. Other aircraft returned damaged.
The G.50bis pilots in return claimed one Gladiator and three PZLs shot down, while the pilots from the 160^o Gruppo submitted claims for three Gladiators (one each by Tenente Crainz, Sergente Maggiore Luciano Tarantini and Sergente Maggiore Aurelio Munich) and two PZLs (Sottotenente Raoul Francinetti and Sergente Antonio Crabbia).
It seems that no Italian fighters were lost on this occasion.

On 10 February four PZL P.24s of 23 Mira together with four PZLs of the 22 Mira and four Gladiators of 21 Mira patrolled near the Premeti area. The Gladiators (Sminagos Kellas, Sminagos Dimitrios Skaltsogiannis, Anthiposminagos Anastasios Bardivilias and Episminias Ilias Dimitrakopoulos) acted as top-cover for the PZLs.
The Greek fighters intercepted three formations of 47^o Stormo Z.1007bis and five S.79s from the 104^o Gruppo, which were out to attack Yanina. It also seem that thirteen BR.20s from the 37^o Stormo were involved in this interception. The Italian bombers were escorted by 154^o Gruppo C.T. G.50bis fighters, led by Maggiore Eugenio Leotta. The 22 and 23 Mire attacked the bombers and the 23 Mira claimed three shot down; one by Sminagos Grigorios Theodoropoulos (CO of 23 Mira), one by Sminago Basileio Skroubelos and one by Yposminago Panagioti Mpousio. One more was claimed as a probable by Sminias S. Depountis. The 22 Mira claimed two more bombers and two probables. Pilot claiming were Sminagos Andreas Antoniou, Yposminago Marino Mitralexi, Sminago Grigorio Fanourgaki (who claimed one of the propables) and Episminia Ioanni Michopoulo.
According to the diary of the commander of 23 Mira, Sminagos Theodoropoulos, the 21 Mira shot down three Italian fighters when they were trying to intercept the PZLs.
Michopoulos was shot down during the combat and he made a forced-landing, but due to the damages on his fighter, it was completely destroyed and the pilot was wounded. Scroubelos’ aircraft was also hard hit although he managed to return to base. Back to base two PZLs were destroyed during landing. However, against all odds and working all the night, the Greek Mechanics, managed to reconstruct a new aircraft from the parts of the two written-off ones, receiving the admiration of the RAF personnel. The Italians claimed four PZLs and one Gladiator. It seems that Maggiore Leotta claimed the shot down Gladiator.

At the time of the German blitzkrieg through the Balkans in April, 21 Mira were stationed at Paramythia and later moved to Kalambaka/Vassiliki.

In the morning on 15 April 18 Ju 87s approached Trikala airfield were the remnants of the EVA fighters had assembled (apart from eight PZL P-24s at Larissa). The Stukas were escorted by around 20 Bf 109Es from II/JG 27. Five Gladiators (flown by Sminagos Ioannis Kellas (CO of the 21 Mira), Sminagos Dimitrios Skaltsogiannis, Sminagos Konstantino Hondros, Sminago Ioanni Papadimitriou and Yposminago Ioanni Katsaro) from 21 Mira were scrambled together with four PZL P.24s from the 22 Mira and two Bloch MB.151s from 24 Mira. One of the Ju 87s was claimed shot down by one Gladiator from 21 Mira while a PZL claimed a second. Two more Ju 87s were claimed as probables by Sminagos George Mokkas of the 24 Mira before Bf 109Es from 4./JG 27 intercepted west of Trikala and Mokkas MB.151 was shot down by Oberleutnant Gustav Rödel (identifying it as a “Hurricane”; this was his 15th victory) at 06:50, killing the pilot. Five minutes later Rödel claimed a PZL and at the same time claimed Oberfeldwebel Otto Schulz another PZL (victory no. 5). A Gladiator was claimed at 07:01 by Leutnant Ernst Börngen (victory no. 3) while Leutnant Wilhelm Wiesinger claimed a second Gladiator at 07:04 (victory no. 8). Rödel claimed his third victory when he claimed another PZL at low altitude (50-100 meters) 10 kilometres north-east of Trikala at 07:05.
Apart from Mokkas, Kellas Gladiator was hard hit and he crashed slightly wounded, his aircraft bursting in flames. Episminias Katsarelis of 22 Mira fought with four Bf 109s claiming to have shot down one, which was supposed to have crash-landed near the airfield, before he was shot down by Schulz. He crash-landed his aircraft, which was totally destroyed but he survived with severe wounds. Episminias Panagiotis Argyropoulos claimed a Bf 109E for his fifth and last victory.
The remaining Greek aircraft were also hard hit and many of them were written-off after landing. The Greek fighter forces had virtually ceased to exist and this was their last combat.
No German losses had been possible to verify with Luftwaffe records.

Later in the war he served as a flight leader at 335 Squadron in Middle East. Here he took part in the preparations and low level bombing of the Italian High Command in Libya in the morning on 28 October 1942 (on the two-year anniversary of the Italian attack on Greece). The bombing attack was successful.

At the end of the war Kellas was credited with 2 biplane victories and a total of 3.

Kellas retired as a Captain in 1948.

Claims:

Kill no.	Date	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1940
1	20/11/40	1	Z.1007bis	Destroyed	PZL P.24		Lake Mikri Prespa	21 Mira
	1941
	25/01/40	1/3	BR.20 (a)	Shared destroyed	Gladiator		Premeti - Kelsyre area	21 Mira
2	09/02/41	1	Enemy fighter (b)	Destroyed	Gladiator		Kelcyre-Tepelene area	21 Mira
3	09/02/41	1	Enemy fighter (b)	Destroyed	Gladiator		Kelcyre-Tepelene area	21 Mira

Biplane victories: 2 and 1 shared destroyed.
TOTAL: 3 destroyed.
(a) Claimed in combat with BR.20s from the 116^a Gruppo, 37^o Stormo B.T. 21 and 22 Mire claimed three bombers. Italian records report two heavily damaged bombers. One forced-landed at Lecce with 3 crew members dead and a second force-landed near Berat.
(b) Claimed in combat with fighters from 24^o and 160^o Gruppi. The 21, 22, 22 Mire claimed eight enemy fighters for the loss of one PZL while several more were damaged. The Italian fighters claimed five PZLs and four Gladiators without loss.

Sources:
Air war for Yugoslavia, Greece and Crete - Christopher Shores, Brian Cull and Nicola Malizia, 1987 Grub Street, London, ISBN 0-948817-07-0
Luftwaffe Claims Lists - Tony Wood
Personal letter to Lars Larsson from Greek Airforce historical archive.
Additional information kindly provided by Dimitrios Vassilopoulos.