Several Facts about the German Invaision of France and the Low Countries .
When the BEF first landed in France the troops were ordered to dig defensive trenches, along the boarder between France and Belgium, but at the same time discussions were ongoing with the Belgium Government, about reconoitering the land to see if there were any good defensive positions in Belgium, because the Britsh and French Plans had their Armies moving into Belgium to counter the German Invasion, but the Belgium Government said no, because they did not want to upset the Germans, over issues of their neutrality.
When the German Invaision happened the Belgium Government, asked the British and French Governments to send their troops into Belgium,
Allied troops then advanced towards a highly trained and Mechanised German Army, with vast Air Support compared to the BEF and French Armies, without the use of a previously prepared defensive system, at which point troops and transport were caught out in the open, beacuse the Belgium Boarder defences had already been broken through.
The Allied Armies held on for a day or two , but then the Germans broke through on the left had side of the BEF (The Belgium Army) , and they subsequently broke through on the Right hand side of the BEF(The French Armies) causing what is now known as the Race to the Channel Ports.
British Senior Officers were sceptical about the advance into Belgium any way as the thought it might be a trap, the thinking at the time was that they should stay where the trenches were , so that they could hopefully hold up the German advance long enough for the front to stabilise , and end up being like the First World War , where you had long periods of stalemate in trench warfare.
Montgomery who was GIC of one of the British Divisions , was very sceptical about the advance into Belgium , and he had his soldiers practicing a withdrawal under fire. Which his Division ended up having to do, while under attack by 3 German Divisions , and this withdrawal was completed succesfully.
After several days of hard fighting the Belgium Government ordered a ceasfire of all their troops , and surrenderd to the German Forces, the Gonvernment having already been evacuated to Britain.
This caused a major problem to General Allenbrooke as he had to fill the hole made by the surrender of the Belgium Forces, so consequently the length of the front covered by the BEF shrunk. and of course after the collapse of the French Forces, you ended up with BEF and some French Forces fighting side by side conducting a slow withdrawal to Dunkirk.
The British Forces did after the Germans had broken through on the right hand side of the BEF, stage a counter attack, but due to there not being enough troops available , they could not hold onto the positions they had taken and retreated back to the BEF Lines, this counter attack worried the German High Comand, and it was responsible for Hitler giving the order for all the German Tanks to stop where they were, when the BEF could have been cut off from Dunkirk and rescue, it was also responsible for the German High Comand to broadcat this message to all Troops "Beware The British they have Teeth".
And as you all know the BEF weere rescued succesfully at Dunkirk, and a few otherplaces along the Channel Coast .
Lord Gort was in comand of the BEF and I think Lord Allenbrooke was 2nd in Command.