The Germans did not attempt a coup de main but waited until the next day and bombarded the forts using super-heavy siege artillery and four batteries on loan from Austria-Hungary.

The defeat of the Fifth Army at the Battle of Charleroi on 21 August prevented the French from advancing further and only one regiment reached Namur as reinforcement.

As it became clear that additional relief forces would not arrive, on 23 August survivors of the Belgian 4th Division withdrew southwards to join the Fifth Army near Saint-Gérard.

Amid the disruption of the new rearmament plan, the disorganised and poorly trained Belgian soldiers would benefit from a central position, to delay contact with an invader but it would also need fortifications for defence, which were on the frontier.

German planning was determined by numerical inferiority, the speed of mobilisation and concentration and the effect of the vast increase of the power of modern weapons.

Frontal attacks were expected to be costly and protracted, leading to limited success, particularly after the French and Russians modernised their fortifications on the frontiers with Germany.

Alfred von Schlieffen, Chief of the Imperial German General Staff) from 1891–1906, devised a plan to evade the French frontier fortifications with an offensive on the northern flank, which would have a local numerical superiority and obtain rapidly a decisive victory.

[7] The forts of the FPN were built to withstand bombardment by 210-millimetre (8.3 in) artillery and were equipped with steam-powered electrical generating plant for lights, pumps and searchlights at a cost 29 million francs.

[7] Provision had been made for the daily needs of the fortress troops but the latrines, showers, kitchens and the morgue had been built in the counterscarp, which could become untenable if fumes from exploding shells collected in the living quarters and support areas as the forts were ventilated naturally.

The super-heavy artillery and engineer units from Liège were sent to Namur along the Meuse valley and the experience gained in the operation against the Fortified Position of Liège, led the attacking troops to take the shortest routes to Namur, which brought the Guard Reserve Corps to the north bank of the Meuse and the XI Corps to the south bank.

Bülow arrived at the headquarters of Gallwitz on 20 August and insisted that the 1st Guard Reserve Division move further round to the north and north-west of Namur, to protect the left flank of the 2nd Army as it wheeled around the fortress.

On the south bank XI Corps repulsed Belgian attacks and reached its assembly areas and established a flank guard at Florée.

As the infantry arrived from Héron, Coutisse, Ohey and Hamois it was to assemble at 11:00 a.m., on a line from Franc to Waret, Vezin, Sclayn, Strud and Les Tombs; in the afternoon the artillery was to commence the bombardment.

Air reconnaissance detected Belgian troops at Cognelée and pontoon bridges at Vépion and Arrêt, either side of Namur and railway traffic to the south-west heading for the fortress.

The Belgians had used the time taken by the siege of Liège to build field fortifications between the forts, particularly on the most vulnerable parts of the perimeter from the north to the south-east.

[16] The bombardment on 21 August was interrupted by fog and by noon the artillery on the north-east and south-east fronts had only fired on forts Marchovelette, Maizeret, Andoy and the intervening ground.

On 22 August the Belgian defenders made two counter-attacks and the 3rd Guard Division was drawn into fighting near Marchovelette, which disorganised the attack and led to a delay until the next day.

Plüskow was ordered to be ready to begin barrage-fire to the south of Namur, to prevent reinforcements reaching the defenders or a retirement by the garrison.

No reply was received by the deadline but to avoid a street battle during the night only a bombardment on the citadel and southern part of the town began.

[20] The German Official Historians wrote in Der Weltkrieg, that the swift capture of Namur had made the French position in the angle of the Sambre and Meuse rivers untenable.

The success was ascribed to the skill of Gallwitz, who reconciled the demands of open and siege warfare, with a plan which was far more effective than the methods used at Liège.

[9] The defenders were driven into the citadel, where there were insufficient sanitary facilities for 500 men and the air became unbreathable, while the German artillery destroyed the forts with plunging fire from the super-heavy howitzers and from the rear.