On September 1st, 1939, two French Army Groups invaded the Eisenpakt. The Deuxième Group d'Armées had a wider front to cover (stretching from Luxembourg to the English Canal), few mechanised units, scarcer air support and less experienced troops. Nevertheless, it was ordered to go on the offensive against the Belgian, Dutch, Luxembourgish and German Armies across the Low Countries. This campaign did not see the widespread and astounding French successes of those across the Rhein, but it was successful at tying down a large number of Eisenpakt forces in a position where, had the Armée Mécanisée been successful in its mission, they would have been surrounded and destroyed.
This campaign was characterised by the ample use of French marines and paratroopers to harass Eisenpakt rear assets, although at the cost of enormous attrition rates. Coastal raids and combat drops wreaked havoc on the largely traditional (uniform and well-organised) Eisenpakt command & control apparatus, as well as their logistics. French marines and paratroopers had no realistic chance of being extracted, so they were trained to fall into the countryside and act as irregular fighters until the French Red Army ran into their positions, alongside local communist partisans which chose to rise in arms.
Another important aspect of this campaign were naval battles between the French Red Navy and the Kaiserliche Marine, during which French submarines, destroyers and naval aviation gave the latter battleship-oriented force a run for its money, limiting it to operations on the North Sea. This was an ironic turn of fate, as many of the tactics employed by France's naval commanders with enormous success mirrored those used by the Kaiserliche Marine to defeat the Royal Navy at the Battle of Jutland, more than twenty years prior. Some historians consider this aspect of the Low Countries Campaign the beginning of the Battle of the Atlantic.
Following Guderian's Counteroffensive, the French Second Army Group ceased major offensive operations, but continued attacking limited objectives. Months later, France focused on the Blitz and the Battle of the Atlantic as its major strategic offensives and its land armies turned to trench warfare, hoping to buy enough time for the Soviets to grind Germany down into dust. Around this time German forces on the western theatre of operations were largely relieved by the British Expeditionary Force, beginning what historians call the Second Slog.