The Potez 631 was the main French night fighter during the Battle of France, but a lack of any useable system for intercepting German raiders meant that it saw little combat at night.
The Potez 63 family was developed in response to a specification issued in October 1934 for a twin-engined fighter capable of acting as a day fighter, a night fighter and a fighter direction aircraft. Potez put forward two versions of the design - the Hispano-Suiza powered Potez 630 and the Gnome-Rhone powered Potez 631. The first prototype was of a Potez 630, but this was soon followed by the Potez 631-01, which made its maiden flight in March 1937. Official trials began in November 1937 (having been delayed after the aircraft made a belly landing during its maiden flight). The successful trials were followed by an order for ten evaluation aircraft, including two new Potez 631s and the refurbished prototype.
In June 1937 the French government issued a letter of intent in which it ordered forty Potez 631s - ten two-seat conversion trainers and thirty three-seat fighters. Although the Gnome-Rhone powered Potez 631 was expected to be the main production version of the aircraft, a shortage of available engines meant that this first order also included eighty Potez 630s.
In May 1938 an order for 125 Potez 633 two-seat bombers was cancelled and replaced with one for the same number of Potez 631s. A third order, for 52 aircraft, was placed in June 1938, bringing the total of aircraft on order up to 10 conversion trainers and 207 operational aircraft. Two small export orders were also received, for one aircraft from Yugoslavia and four aircraft from China.
Two export orders were also received, one for four aircraft from China and one for a single aircraft for Yugoslavia. Neither of these orders were fulfilled, although the aircraft destined for China did reach the Far East. They were then seized by the French in Indo-China at the start of the war in Europe. In September 1940 they took part in the short three-day conflict after the Japanese invaded Tonkin.
Service Record: Armée de l'Air
The Potez 631 was introduced into service slightly begin the Potez 630. On 1 January 1939 only 27 Potez 631s had been accepted by the air force, rising to 67 aircraft on 1 April, and 206 in August, completing the production run.
The Potez 631 entered service with the fighter director flights that were attached to each single-engine fighter wing (Escadre de Chasse), and with the night fighter groups (G.C.N. or Groupes de Chasse de Nuit). At the start of the Second World War a total of 206 aircraft had been accepted and 117 had reached front line units. G.C.N. I/13 and G.C.N. II/13 had 39 aircraft, four were in Djibouti, four were at Ajaccio and 70 were with the Escadre de Chasse (alongside a number of Potez 630s). A small number had also gon to GC II/8 where they replaced the Morane-Saulnier MS 225 and Dewoitine D.510 single-seat fighters.
Phoney war period
The allocation of Potez 631s changed significantly during the Phoney War period. At the very start of the war a new Escadrille de Guet (warning) I/16 was formed using aircraft from GC II/8 and from the fighter direction flights. This unit became E.C.M. I/16 (Escadrille de Chasse Multiplace) on 29 January 1940.
In October a fifth night fighter unit was formed around the Potez 631. Originally designated as E.C.N. 2/562, on 1 January 1940 this was redesignated as E.C.N. 5/13. This was part of a wider reorganisation of the French Air Force, which saw the Escadres split into their component escadrilles and the smaller units formed into more flexible groupements. In the case of the night fighters Ecscadre de Nuit 13, which had consisted of G.C.N. I/13 and G.C.N. II/13 was split into E.C.N. 1/13 to E.C.N. 4/13. These units were allocated to the defence of Paris.
On 17 January 1940 the French Naval Air Arm (Aéronavale) received eight Potez 631s, which replaced the Dewoitine D.376 C1 parasol fighters of Escadrille de Chasse AC1. Another seventeen aircraft were received in the spring and were used to equip Escadrille de Chasse AC2. The two escadrilles then formed Flotille F1C, based at Calais-Marck.
In February 1940 the fighter director flights were disbanded. Their Potez 630s became training aircraft, while their Potez 631s were used to increase the official number of aircraft in each night fighter escadrille from 12 to 18.
The spring of 1940 also saw a belated attempt to improve the armament of the Potez 631. Although the type was meant to have two forward firing 20mm cannon these had been in short supply, and a number were built with one cannon and one machine gun. It was now decided to fit every aircraft with the two 20mm cannon and to add four machine guns under the wings. Although this decision was made on 8 February, by 10 May only two up-gunned aircraft had reached the front line.
Battle of France
On 10 May 1940 the Armée de l'Air had 75 Potez 631s in front line units, with 53 of them serviceable. Four night fighter units were allocated to the defence of Paris and the fifth to the defence of Lyons, Etienne and the Le Creusot area. The day-fighter unit E.C.M. I/16 was at Wez-Thuisy. Finally the navy's Flotille F1C was at Calais.
This naval unit was the most successful Potez 631 unit of the Battle of France. Between 10-21 May it shot down 12 German aircraft over the North Sea, losing eight Potez 631s. The unit then withdrew to convert to the Bloch 151 and Dewoitine 520, and didn't return to the fighting.
The five night fighter units were not a success. They began to fly night operations on 11 May, but there were no successful interceptions during the first week of operations. The French High Command then decided to try and use the aircraft in the increasingly desperate day battle. On 17 May twenty-four Potez 631s from the units based around Paris attempted to attack German columns around Formies. Eighteen aircraft reached the target area, and six were lost, probably all to German flak.
The night fighter units achieved their first success on 18 May, when an aircraft from E.C.N. 1/13 shot down a Heinkel He 111. Sadly on the same day the aircraft's resemblance to the Bf 110 resulted in Potez 631 being shot down by a M.S. 406 after being attacked by German fighters and French flak. Another Potez was shot down by three Bloch 152s on 23 May, and on the following day the Armée de l'Air ordered recognition stripes to be painted on each aircraft (5m long white stripes on the fuselage).
From 20 June the night fighter units were forced to retreat south to escape the advancing Germans. At the end of the Battle of France the five night fighter units claimed four confirmed victories and eight probables, but at the cost of ten fighters lost to enemy action and three to friendly fire.
The Potez 631 remained in use in small numbers with the Vichy Air Force. Two night fighter units, E.C.N 1/13 and E.C.N. 3/13 kept the aircraft. Eighty two aircraft were on strength on 1 November 1941, and 64 one year later. They didn’t play any significant part in the short-lived French resistance to Operation Torch. This triggered a German invasion of Vichy France in which they captured a number of Potez aircraft, but while the Potez 63.11 saw some service with the Luftwaffe, the same was not true for the Potez 631.
In the aftermath of the Allied invasion of North Africa and the German occupation of Vichy France, the French units in North Africa changed sides. The Potez 631s of E.C.N. 3/13 were used to defend the Gabès area against German attack, but were replaced with more modern aircraft later in November 1942.
Three Potez 631s were used by the French Forces of the Interior after the Allied invasion of the south of France. They were allocated to Groupe de Reconnaissance II/33 'Périgord' at Cognac, and were used to fly reconnaissance missions over the remaining German pockets of resistance on the Atlantic coast of France. After the war the same aircraft were used as trainers.
Engine: Gnome & Rhone 14 M4/M5 or M6/M7 engines
Power: 570hp at sea level, 660hp at 16,400ft, 700hp at take-off
Crew: 2 or 3
Wing span: 52ft 6in
Length: 36ft 4in
Height: 11ft 10 1/2in
Empty Weight: 5401lblb
Loaded Weight: 8289lb
Max Speed: 275mph at 15,768ft
Cruising Speed: 149mph at 6,234ft
Range: 758 miles
Armament: Two forward firing 20mm cannon (one cannon and one machine gun on some aircraft), one flexibly mounted rear firing 7.5mm machine gun