developments necessitated adjustments to the forts. From 1890 fixed artillery was used. Partly, the artillery was placed in turrets, partly mounted separately. From 1890 the thickness of the concrete vaults was brought up to 2.25 to 2.5 m. The heaviest guns at the time were 21 cm (Krupp) or 22 cm (mortar Le Creusot). The forts had to be able to resist shells of this caliber. However, the developments went very fast. In 1905 the Japanese during the siege of Port Arthur used 28 cm guns. Shortly before the First World War Germany already had 30.5 and even 42 cm caliber ( "Big Bertha "). Trials in Russia in 1912 with a Belgian turret showed that it could not withstand 28 cm guns. Although the military leadership was aware of it, this information was ignored. The military could do nothing, since further modifications to the forts were not possible. The Belgian forts did not have such heavy artillery as the Germans. Because they had a defensive purpose, the heaviest artillery gun used was 15 cm caliber. Only the fortifications for the Scheldt defence (forts De Perel, St. Philip) had 24 and 28 cm guns and Fort Schoten had 21 cm guns. The forts around Liege and Namur had 21 cm howitzers, but with relatively limited range of 6.9 kilometers. The armament of the forts of the outer circle (Act of 1906) for the long range consisted of one or two turrets with two 15 cm guns (39 kg shells, with a range of 8.4 kilometers), two turrets for a 12 cm howitzer (20 kg shells, range 6.4 kilometers), four or six gun turrets for a 7.5 cm gun, (5.5 kg shells; range 6 km), two observation clocks. In addition there was a ditch defence of sixteen 5.7 cm guns (2.7 kg shells, range 2.2 kilometers, especially used with grape-shot for the short range) and support fire between the forts (two 7.5 cm and two 12 cm guns). First World War At the outbreak of war in 1914, the Germans first attacked the forts at Liege. The Germans were equipped with 30.5 cm (Skoda M1911 howitzers lent by Austria, with a range of 9.6 kilometers) and 42 cm (the Big Bertha, range 10 km) caliber guns, with shells respectively 380 kg and 1000 kg. These were able to destroy the fortresses of non-reinforced concrete. They could be deployed while outside the