The Maginot Line was criticised for not continuing all the way to the Channel coast, but that's a harsh judgement.
Military thinking at the time was "if the Germans try to outflank the Line by going through Holland and Belgium, they'll never do it because most of the French Army (millions of men) will be densely concentrated along the short length of frontage between the Line and the coast, and the Germans will never get through".
That would have been true except for one thing- the new Blitzkrieg concept whereby the main spearhead was directed at a very narrow sector in overwhelming strength, guaranteed to pierce any 1940 defence.
Later of course, the Russians showed how to stop the Blitzkrieg by placing masses of tanks and AT-guns in the path of the spearpoint.
While German forces were concentrated on Poland, anxiety was rising on the Western Front, with French troops welcoming British soldiers as they deployed along the border with Germany. Here, French troops pose in a cantonment in France on December 18, 1939.
Members of the French Army man an acoustic locator device on January 4, 1940. The device was one of many experimental designs, built to pick up the sound of distant aircraft engines and give their distance and location. The introduction and adoption of radar technology rendered these devices obsolete very quickly.
A party of newspaper men on the Western Front are shown atop one of the big forts somewhere in the Maginot Line, France, on October 19, 1939, with a French army guide pointing out to them the "no man's land" that separates the French and German troops.