The French defences at Sedan were weak and neglected.
The French had long believed that the German Army would not attack through the Sedan sector as part of their concentrated effort, and only Brigadier General Pierre Lafontaine's French 55th Infantry Division, a category B division, was allocated to this sector.
The Maginot Line ended 20 kilometres (12 mi) east of Sedan at La Ferté, where Fort No.
505 constituted its most westerly position.
Sedan was a part of the extended Maginot Line that ran north behind the Meuse river.
Between Sedan and La Ferté lay the Stenay gap, which was a stretch of unprotected terrain not covered by French defences or natural obstacles.
This was the reason a significant number of French generals insisted on strengthening this sector, while ignoring Sedan.

As the French constructed further fortifications, Luftwaffe reconnaissance aircraft picked up the activity and reported it.
The steep slopes on the banks of the Meuse, added to what appeared in photographic reconnaissance to be a formidable barrier of bunkers and defence lines, caused Field Marshal Gerd von Rundstedt, the commander in chief of Army Group A, to question the wisdom of Guderian in choosing Sedan as the point of maximum effort.
To identify how strong these fortifications were, a team of photographic specialists were called in to evaluate the pictures.
Their analysis concluded that what appeared to be strong fortified positions were just the construction sites of half-built bunkers that were, to all intents and purposes, empty shells.
The contribution of the specialists tilted the Sedan attack plan into Guderian's favour.

General Huntziger was happy to rely on "concrete" to ensure the safety of Sedan as he rejected the idea that the Germans would attack through the Ardennes.
The Second Army built 52,000 cubic metres (1,800,000 cu ft) of concrete fortifications along its front, but very little in the Sedan sector.
Only 42 bunkers protected the Sedan bridgeheads on the outbreak of war in September 1939 and an additional 61 were built by 10 May. However, by 10 May, most of the bunkers were incomplete, lacking gun port shutters for the artillery casemates.
Some of the bunkers lacked rear doors, making them vulnerable to infiltration by infantry.
To the north of Sedan, on the northern bend of the Meuse, the town of Glaire overlooked the crossing points on the river, which was to be where the German armour would deliver its heaviest blow.
There was a gap of 2 kilometres (1.2 mi) between Bunker 305 at Glaire and Bunker 211 next to the Pont Neuf bridge.
This allowed an attacker coming from the north to use the good road routes through the Fleigneux–Saint-Menges–Glaire axis to enter Sedan from the north.

The defences at Sedan also lacked any mines.
The French Second Army was guarding a front of 70 kilometres (43 mi), and was given only 16,000 mines.
Of that number, 7,000 were given to the cavalry divisions that were intended to delay a German advance through southern Belgium as well as to blockhouse points along the Franco–Belgian border.
That left 2,000 for the defence of the river Meuse.
Of those, the 55th Infantry Division got 422.
Not all of these were laid, and some barriers were moved during the bunker construction in the Sedan sector.
The French defences at Sedan were weak and neglected. The French had long believed that the German Army would not attack through the Sedan sector as part of their concentrated effort, and only Brigadier General Pierre Lafontaine's French 55th Infantry Division, a category B division, was allocated to this sector. The Maginot Line ended 20 kilometres (12 mi) east of Sedan at La Ferté, where Fort No. 505 constituted its most westerly position. Sedan was a part of the extended Maginot Line that ran north behind the Meuse river. Between Sedan and La Ferté lay the Stenay gap, which was a stretch of unprotected terrain not covered by French defences or natural obstacles. This was the reason a significant number of French generals insisted on strengthening this sector, while ignoring Sedan.
As the French constructed further fortifications, Luftwaffe reconnaissance aircraft picked up the activity and reported it. The steep slopes on the banks of the Meuse, added to what appeared in photographic reconnaissance to be a formidable barrier of bunkers and defence lines, caused Field Marshal Gerd von Rundstedt, the commander in chief of Army Group A, to question the wisdom of Guderian in choosing Sedan as the point of maximum effort. To identify how strong these fortifications were, a team of photographic specialists were called in to evaluate the pictures. Their analysis concluded that what appeared to be strong fortified positions were just the construction sites of half-built bunkers that were, to all intents and purposes, empty shells. The contribution of the specialists tilted the Sedan attack plan into Guderian's favour.
General Huntziger was happy to rely on "concrete" to ensure the safety of Sedan as he rejected the idea that the Germans would attack through the Ardennes. The Second Army built 52,000 cubic metres (1,800,000 cu ft) of concrete fortifications along its front, but very little in the Sedan sector. Only 42 bunkers protected the Sedan bridgeheads on the outbreak of war in September 1939 and an additional 61 were built by 10 May. However, by 10 May, most of the bunkers were incomplete, lacking gun port shutters for the artillery casemates. Some of the bunkers lacked rear doors, making them vulnerable to infiltration by infantry. To the north of Sedan, on the northern bend of the Meuse, the town of Glaire overlooked the crossing points on the river, which was to be where the German armour would deliver its heaviest blow. There was a gap of 2 kilometres (1.2 mi) between Bunker 305 at Glaire and Bunker 211 next to the Pont Neuf bridge. This allowed an attacker coming from the north to use the good road routes through the Fleigneux–Saint-Menges–Glaire axis to enter Sedan from the north.
The defences at Sedan also lacked any mines. The French Second Army was guarding a front of 70 kilometres (43 mi), and was given only 16,000 mines. Of that number, 7,000 were given to the cavalry divisions that were intended to delay a German advance through southern Belgium as well as to blockhouse points along the Franco–Belgian border. That left 2,000 for the defence of the river Meuse. Of those, the 55th Infantry Division got 422. Not all of these were laid, and some barriers were moved during the bunker construction in the Sedan sector.
Battle of Sedan (1940)