Siege of Antwerp The Siege of Antwerp was an engagement between the German and the Belgian armies during World War I . A small number of British and Austrian troops took part as well . Strategic Context . The German army invaded Belgium on the morning of August 4 , 1914 , two days after the decision of the Belgian government not to allow German troops unhindered passage to France . The Belgian army found itself desperately outnumbered by the Germans and was limited to conduct a fighting retreat from the onset of the invasion . Early on in the campaign , the Belgian army had to relinquish control of the fortified cities of Liège ( August 16 ) , the capital Brussels ( August 20 ) , and Namur ( August 24 ) . The city of Antwerp was defended by numerous forts and other defensive positions and was at the time considered to be impenetrable by a conventional ground attack . Since about 1860 , the Belgian defence doctrine was centered on a retreat to Antwerp to hold off any aggressor until the European powers guaranteeing Belgium ' s neutrality would be able to intervene . When it became apparent that the Belgian field army would be unable to withstand the massive German offensive , King Albert I of the Belgians implemented the plan to defend the country and instructed a withdrawal to the " National Redoubt of Antwerp " on August 20 . The Belgian government subsequently moved from the capital Brussels to Antwerp to avoid their capture by the advancing Germans . Fortifications . The " National Redoubt " consisted of four defensive lines : Most forts were of mid - 19th century construction , but most were modernised in the years leading up to the conflict . A number of forts of the principal line of resistance were of modern reinforced concrete construction . The German attack and siege . After the retreat of the Belgian army into Antwerp , the German imperial high command initially detached only the 3rd Reserve Corps of the 1st Army to the city as a covering force . The Belgian army was committed to offering strategic support to its French and British allies and conducted two sorties out of Antwerp to force the German army to detach additional troops to the siege and to harass the enemy lines of communication during the battle of the Marne . A first sortie on August 25 and 26 and a second raid from September 9 to September 13 forced the German army to make significant troop diversions from the front line in France to Antwerp . The Germans were defeated on the Marne on September 12 . The order to launch an all - out attack on the city came on September 7 , when the heavy siege artillery units had become available following the siege of the French forts of Maubeuge . The German Army launched a first artillery bombardment on September 28 , and made some immediate and important gains . The defenses were unable to withstand German 42 cm " Big Bertha " howitzers ( not to be confused with the later Paris Gun ) and Austrian 30 . 5 cm howitzers . From the onset of the main assault it became apparent that the Belgian army would not be able to hold out for any substantial length of time . Moreover , the continuing advance of the German army through Belgium and France threatened to cut off any escape route from the city . On October 1 the Belgian government sent a telegram to the British announcing that they would retreat from Antwerp in three days time . The British government allowed the First Lord of the Admiralty Winston Churchill to go over to establish which assistance would be required to strengthen the Belgian defences . He telegrammed back that Antwerp would have to be reinforced and then relieved . On the night of October 3 a brigade of Royal Marines arrived as the first element of the Royal Naval Division . This was a great morale boost to the Belgians , but failed to alter the predicament of the city . October 5 was a crucial date during the Siege of Antwerp ; the German army broke through the Belgian defences in the city of Lier , 20 kilometers southeast of Antwerp and moved on to the town of Dendermonde ( south of Antwerp ) where it attempted to cross the river Scheldt . This pincer movement of the German army threatened to block the western retreat route of the Belgian army out of Antwerp . With its eastern and southern flanks being blocked by German troops and its northern escape route closed off by the Belgian - Dutch border , the Belgian army evacuated Antwerp via a series of pontoon bridges over the Scheldt and left the city to its own defenses . The last Belgian elements of the field army fled westwards towards the coast on October 8 and the Germans entered the city on October 9 after having established that the defensive positions had been abandoned . The Belgian Lieutenant - General Deguise offered the unconditional surrender of the remaining garrison troops . A substantial number of Belgian troops and elements of the Naval Division fled into the neutral Netherlands and ended up being interned for the duration of the war . Aftermath . The mayor of Antwerp , Jan De Vos , offered the formal capitulation on October 10 and the Siege of Antwerp was over . The city of Antwerp would remain occupied by German troops until November 1918 . One third of the Belgian Army , about 30 , 000 soldiers , fled north to the Netherlands , followed by about one million civilian refugees in 1914 who , depending upon their means of transport , ended up in Great Britain , the Netherlands and France . The Netherlands interned Belgian soldiers as far as possible from the Belgian border , for fear of being drawn into the conflict . A sizable number of the refugees continued living in the Netherlands after 1918 and never returned to Belgium , but the majority returned to Belgium in the weeks following the capture of Antwerp by the Germans . The Belgian Army eventually stopped the German advance on the banks of the river Yser .