Alexander Ermoshenko via ReutersThe Azovstal Metallurgical Plant, a symbol of Ukrainian resistance in Mariupol (Photo of Mariupol with the Azovstal plant in the background, taken March 28, 2022. By REUTERS/Alexander Ermoshenko)WAR IN UKRAINE – Even if the The city’s downfall seems inevitable, Mariupol has yet to fall to the Russians, and resistance continues at the iconic Azovstal factory. Indeed, the Russian army blocks on a group of fighters hidden in the tunnels of this vast industrial complex. The fight for this strategic port city takes place in an area of over 11 km² along the Sea of Azor. An area crossed by railways, warehouses, coke ovens, various factories and chimneys. Reduced visibility, holes, obstacles, traps at every step, steel and concrete as far as the eye can see, are the lot of the fighters on the spot. But it’s under the surface that everything is happening: the Azovstal factory hides a real city made up of underground networks. Sources evoke more than 20 kilometers of tunnels, up to 30 meters deep. The information could not be verified by AFP from a reliable source, while the last Western journalists left the city in mid-March. In any case, it is here that part of the Ukrainian army has withdrawn and has continued to resist Russian attacks for weeks. A shelter for the Ukrainian servicemen, the Azov battalion and a thousand civiliansAzovstal was originally built in the early Soviet era and was later rebuilt after the Nazi occupation of Mariupol between 1941 and 1943 left it in ruins, notes the Washington Post. It is owned by the Metinvest group, controlled by Ukraine’s richest man, Rinat Akhmetov. As one of Europe’s largest metallurgical plants, it normally processes more than 4 million tons of steel gross per year and employs tens of thousands of people. With HuffPost’s daily newsletter, receive the most important news and the best articles of the day by email. Read more However, the military are not the only ones to use the factory as protection since no less than 1,000 civilians are also hiding in the underground network, according to the Mariupol city council.A highly advantageous strategic configuration… It must be said that this underground maze offers ideal protection and an almost perfect strategic fallback point. How to represent the industrial zone? “It’s a city within a city, and there are several underground levels from the Soviet period, it’s not possible to bomb from above, you have to clean underground. It will take time,” admitted Edouard Basurin, representative of pro-Russian separatist forces in Donetsk, at the end of March. via Associated PressAerial view of destroyed eastern Mariupol, April 9, 2022. For Russian forces, entry into the tunnels is “impossible”, confirms Alexander Grinberg, an analyst at the Jerusalem Institute for Security and Strategy (JISS). They “can try to do it, but they will be slaughtered because the tunnel defenders have the absolute tactical advantage”. Because the tunnels remain very effective in creating uncertainty for the adversary. They reduce the effectiveness of enemy artillery, airstrikes, infantry, snipers. They impose silence on satellite surveillance and complicate technical intelligence by offering combatants in the lowlands a real ability to move. But “the network really has to be very dense. They must also have stored ammunition, food and drink. That means a big preparation phase,” a French military official told AFP. James Rands, analyst for the private British intelligence institute Janes, mentions in particular the necessary and delicate training of soldiers. “Closing spaces leads to close-range combat, limiting the effectiveness of certain weapons,” he notes. Explosives increase in power, but the blast effect can backfire. At the tactical level, “command and control is extremely difficult. Standard communications don’t work well and situational awareness is low as the tunnels are generally poorly mapped,” adds James Rands. Not to mention the hell of medical evacuations. In theory, “an hour of progress in an underground network costs ten hours in evacuating victims”, according to him. The rifts of the fortress “These are huge territories with workshops that cannot be destroyed from the air, c That’s why the Russians use heavy bombs,” military analyst Sergiy Zgurets told the Guardian. But is this underground citadel impregnable? This would require that the Ukrainian forces have a sufficient quantity of all the necessary equipment, such as night vision goggles. And this is probably not the case. And they will have to compensate for the possible use by the Russians of water, to drown the tunnels and the fighters who are there, or of gas and other chemicals, to make unbearable or even impossible all life inside. “That’s why the Russians started talking about a possible chemical attack; it’s the only way to smoke them out,” said Oleh Zhdanov, a Kyiv-based military analyst quoted by The Guardian. On this subject, the United Kingdom announced on April 12 that it was trying to verify information on the possible use of chemical weapons in Mariupol. Which has not yet been confirmed. Mariupol, with a pre-war population of around 450,000, is one of the last urban areas in Donetsk not to be fully under Russian control. Its capture would give Russian forces a land bridge between Russia and Crimea, the peninsula it annexed from Ukraine in 2014. Also see on The HuffPost: Ukraine: Six dead in ‘powerful’ missile strikes on Lviv