French troops were sent into the area, as Général d'armée Maxime Weygand attempted to build up a defence in depth on the south bank of the Somme and make bigger attacks to eliminate the German bridgeheads.

When Fall Rot (Case Red), the final German offensive, began on 5 June, the IX Corps of the French Tenth Army (including the 51st (Highland) Infantry Division (Major-General Victor Fortune) of the British Expeditionary Force (BEF) after it arrived from the Saar on 28 May), was pushed back to the Bresle River.

Within a few days, Army Group A (Generaloberst Gerd von Rundstedt) broke through the French Ninth Army (General André Corap) in the centre of the French front near Sedan and drove westwards down the Somme river valley, led by Panzergruppe Kleist made up of the XIX Armeekorps under Generalleutnant Heinz Guderian and the XLI Armee Korps under Generalleutnant Georg-Hans Reinhardt.

The Battle of Arras, a Franco-British counter-attack on 21 May, led the Germans to continue to attack north towards the channel ports, rather than advance southwards over the Somme.

On 5 June, the German 4th Army attacked out of the remains of their bridgeheads south of the Somme and the Franco-British divisions opposite, drastically depleted by their counter-attacks of the previous four weeks, were pushed back to the Bresle with many casualties.

The plan was based on the traditional concept of Vernichtungsgedanke (annihilation theory) in which Bewegungskrieg (battles of manoeuvre) would lead to the encirclement and destruction of the opposing armies.

Despite protests from Guderian, List planned the attack over the Aisne as an infantry operation, with the panzer divisions held back to exploit the breakthrough.

[10] The Luftwaffe made strategic attacks from 1–4 June (towards the end of the Dunkirk evacuation), against the Parisian aircraft industry and fuel dépôts around Marseilles, then resumed close support operations for the army for Fall Rot.

[12] On 5 June, Fall Rot (Case Red), a German offensive to complete the defeat of France began and Army Group A attacked either side of Paris towards the Seine.

The French 31st (Alpine) Division was forced back parallel to the British from Limeux to Limercourt and Béhen, with the 152nd Infantry Brigade on the right from Oisemont to the Blangy–Abbeville road.

Earlier, 12 Blenheims with air cover flew from England to attack German columns moving towards the Somme crossings and lost five aircraft.

[20] During the evening, Général d'armée Maxime Weygand, arrived at the Tenth Army HQ and told the Franco-British officers that the Tenth Army was fighting the decisive battle of the war, that as there were no reserves and all depended on the 1st Armoured Division holding 10 mi (16 km) of the Andelle line from Nolleval to Serqueux, as French formations counter-attacked from the south.

The 1st Armoured Division had been broken up as soon as it arrived in France and without the detachments to Calais had taken part in the Allied offensive against the German bridgeheads south of the Somme.

Ihler received the orders as the Tenth Army HQ was out of touch while moving closer to Paris and gave the divisional commanders a retirement programme in which Rouen was to be reached in four days, despite the German spearheads being only four hours from the city.

The panzer divisions had turned north from Rouen towards Dieppe and captured the Arkforce wireless lorry near Carny on the Durdent river at 11:00 a.m.

Units were ordered to dump non-essential equipment and guns were reduced to 100 rounds each to make room on the RASC transport for the men.

French transport continued to arrive at the perimeter and it was difficult in some places to recognise German troops following up, which inhibited defensive fire.

Near dawn, the troops at the harbour were ordered back into the town and at 7:30 a.m., Fortune signalled that it might still be possible to escape the next night, then discovered that the local French commander had negotiated a surrender.

[31] A Royal Navy demolition party had been in Le Havre since late May and the port was severely bombed by the Luftwaffe on 7 June; two days later, the Admiralty sent orders for an evacuation.

[32] A hasty plan was made to block Dieppe harbour and on 10 June, HMS Vega (Captain G. A. Garnon-Williams) escorted three blockships to the port.

[32] (James had signalled that many IX Corps troops would probably be trapped against the sea near St. Valery, where he had assembled flotillas of smaller craft under the local Senior Naval Officer.

The embarkation was hindered somewhat by the damage to the port caused by Luftwaffe bombing; the troopship SS Bruges, was hit and beached, the electric power was also cut, rendering the cranes on the docks useless.

Late on the third day of the offensive the Germans managed to cross the Somme and Aisne despite bombing by the Armée de l'Air (French Air Force).

Beauman, Evans and Marshall-Cornwall discussed the find at the Tenth Army HQ but Karslake was omitted, despite being the senior British officer in France.

Karslake had already made representations to the CIGS about the lack of unity of command but on 6 June, Dill had written to the Swayne Mission at Georges's HQ that Brooke could be expected the following week and that the 52nd (Lowland) Division was due soon.

The II Corps headquarters had been spread around Britain after its return from Dunkirk and his first choice of chief of staff was busy with Lord Gort the former BEF commander, writing dispatches.

The German advance threatened the airfields of the AASF, which was ordered to retreat towards Nantes or Bordeaux, while supporting the French armies for as long as they kept fighting.

The army was ordered to retreat to a line from Verneuil to Argentan and the Dives river, where the British took over an 8 mi (13 km) front, either side of the Mortagne-au-Perche–Verneuil-sur-Avre road.

That day, the Anglo-French Supreme War Council met at Briare and General Charles de Gaulle (Minister of War) was sent to Rennes to survey progress on the redoubt; on 12 June, De Gaulle reported that Quimper would be a favourable place for the government to retreat to, since it would be easy to take ship to England or Africa, since the prospect of maintaining a redoubt in Brittany was non-existent.

Brook telephoned Dill in London to find that no agreement had been made with the French and after checking called with the news that "Mr. Churchill knew nothing about the Brittany project".