Romulo Negrin Mijoilar was the son of the prime minister of the Republic of Spain.

In January 1938, Negrin served in the 4^a Escuadrilla of the Grupo de Caza N^o 26, equipped with Polikarpov I-15s.

On 17 January, there were three clashes between Republic and Nationalist aircraft. In the last combat two groups of I-15s (32 fighters) were out to strafe in the Teruel area, escorted by eight I-16s. Over the target they clashed with a formation of 15 He 111s and 40 Fiat CR.32s. Two I-15s were quickly shot down when Leitenant Aleksandr Osipov (patrulla CO 1^a/26 in I-15 CA 007) was shot down by fighters but managed to parachute and land in friendly territory. The second was Kapitan Yevgeniy Stepanov of the Grupo N^o 26, who was shot down by AA fire over the town of Ojos Negros but managed to bale out. He was taken prisoner and spent the next six months in various prisons (Zaragoza, Salamanca and San Sebastian). One I-16 was shot down and the pilot killed. A third I-15 made a “taran” and the pilot, Negrin (the son of the prime minister of the Republic of Spain), who served in the 4^a/26, was wounded. He had attacked some Fiats, which were attacking Stepanov hanging in his parachute, bringing one of the CR.32 down together with his own fighter; the Italian pilot was killed. Two more I-15s were damaged in forced landing due to lack of fuel and five more returned with battle damage.
Teniente Leopoldo Morquillas Rubio, CO 2^a/26 claimed a CR.32 shot down during the day in the Teruel area as did J. Vela Díaz and C. Zuazo Garre from the same unit.
The Republican side claimed four Fiat CR.32s and one bomber. Two more CR.32s were claimed as damaged or probably destroyed.
The Italians from VI Gruppo claimed 11 ‘Curtiss fighters’ but lost two pilots when Maresciallo Bruno Cesna, (33^a Squadriglia) and Sergente Maggiore Angelo Boetti (Staff of VI Gruppo) were killed while Sergente Benassi was wounded. One Spanish pilot was also shot down when Pedro Gil Escosin was shot down in his Fiat CR.32 and parachuted. In one of the He 111, one of the crew members, T. Martner, was so badly wounded that he died the next day in hospital.
While as prisoner Stepanov was taken out to be shot on three occasions. The Republican government eventually managed to exchange him via the International Red Cross for some German PoWs.

On 10 March, K/88 made three missions. During the first and taking off from Alfaro at 06:00, the four staffeln joined to attack Candasnos. At about the same time, the Do 17s of A/88 took off from Bunuel and all four staffeln of the Jagdgruppe took off from Sanjuro. At 07:00, the bombers of K/88 arrived over the Republican airfields at Caspe, Sarinena and Candasnos. Conditions were hazy. At Caspe five enemy aircraft were claimed destroyed on the ground. The airfield of Bujaraloz were bombed by the Do 17 Staffel and soon afterwards was forced to endure a low-level strafing attack by several He 111s. Returning from a high-level attack on Candasnos, the Heinkel bombers roared over Bujalaroz with all guns blazing. The He 111 unit set course for home leaving one parked aircraft in flames. It seems that He 111 25-7 from 4.K/88 returned for a second attack when it was attacked from behind and below by an I-15 just as it had crossed the airfield and forced to land at Bujaraloz (20km from Candasnos). The crew of Feldwebel Willi Hesse (pilot), Unteroffizier Theo Kowollik (radio operator), Unteroffizier Karl Hoffmeister (engineer, who reported that he couldn’t fend of the attack due to a jamming gun), Leutnant Kurt Kettner (commander and observer) and Obergefreiter Heinz Clacery (observer and had been invited for the trip) all became PoWs (they were exchanged on 2 Janaury 1939). This was the only He 111 lost during the day.
Flying from Candasnos, the 4^a/26 scrambled nine I-15s at 06:45 to intercept them and claimed two He 111s shot down over the airfield, one of which was credited to capitán Ladislao Duarte Espés (CO) for his last aerial success of the civil war. Negrin also took part in this intercept flying in CC-011.
I-16 CM-141 from 1^a/21 was destroyed by fire at Caspe during the day.

In August 1938, Negrin was sent to the USSR to take part in a higher command course. It seems that he was still in the USSR when the war ended and he later took part in the Second World War with this country.

Negrin ended the Spanish Civil War with 1 biplane victory.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1938
1	17/01/38		1	CR.32 (a)	Destroyed	I-15		Teruel area	4a/26

Biplane victories: 1 destroyed.
TOTAL: 1 destroyed.
(a) Claimed in a “taran” ramming attack. Republican pilots totally claimed 4 and 2 damaged CR.32s and 1 bomber while losing 2 I-15s, 1 I-16 and getting 2 I-15s damaged. VI Gruppo claimed 11 I-15s while losing 3 CR.32s (2 pilots KIA). 1 He 111 was damaged.

Sources:
Air War over Spain - Jesus Salas Larrazabal, 1974 Ian Allan Ltd, Shepperton, Surrey, ISBN 0-7110-0521-4
Fighter Pilots Of The Spanish Republic (Vol. 1) - Rafael A. Permuy López, Historica 36/39 no. 1, ISBN 84-87314-89-9
Legionaire Ace – Julius R. Gaal, 1972, Aero Album Volume 5 Number 1 Spring 1972
Polikarpov I-15, I-16 and I-153 Aces - Mikhail Maslov, 2010 Osprey Publishing, Oxford, ISBN 978-1-84603-981-2
Soviet airmen in the Spanish civil war 1936-1939 - Paul Whelan, 2014 Schiffer Publishing Ltd, ISBN 978-0-7643-0
Spanish Republican Aces – Rafael A. Permuy López, 2012 Osprey Publishing, Oxford, ISBN 978-1-84908-668-4
Wings Over Spain - Emiliani Ghergo, 1997 Giorgio Apostolo Editore, Milano
Additional information kindly provided by Alfredo Logoluso and Ondrej Repka.