Prague’s underground infrastructure forms a network of protective lines capable of sheltering residents in times of crisis and war. Similar to larger cities with metro systems, Prague has many tunnels, service passages, and rooms of various sizes and purposes. However, there is also a hidden part of the metro that hundreds of thousands of people traveling between work and home every day do not notice.

This is because most of the Prague metro, the capital of the former Czechoslovakia, whose first line opened in 1974,¹ was built during the Cold War, and as work progressed, a project called OSM was launched, the nature of which was perfectly concealed by the metro construction. It is estimated that the Ochranný Systém Metra protection system, which covers most of the metro as a giant shelter, accounted for nearly half of the construction cost of the underground railway. Half a century later, it can still accommodate nearly 330,000 people, or one in four of the capital’s residents.

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OSM qualifies as a STOU (Stálý Tlakově Odolný Úkryt, or permanent pressure-resistant shelter)² shelter in the Czech Republic and, similar to higher-category shelters in Finland, protects against shock and pressure waves, radiation and radiation contamination, heat pulses, and chemical and biological weapons. This is made possible by the depth (the deepest station is 55 meters below ground) and practical solutions that allow most of the metro system to be hermetically sealed with special doors in case of danger, as in Finland.

STOU stations have blast doors that separate the tunnel sections, and there are even more of them in the tunnel network itself, which means that the destruction of one area will not cause a domino effect in other sectors, and they will remain safe. The STOU stations that offer the highest level of protection are on line A from Dejvicka to Skalka (12 stations with a capacity of 116,000 people), on line B from Nové Butovice to Českomoravská (14 stations, 130,000 people) and on line C from Roztyly to Háje, plus the Vltavská and Nádraží Holešovice stations (a total of 6 stations for 85,500 people).³

This brings us to the current situation in the Czech Republic, where Prague’s 65 km long metro system forms a significant part of a proper shelter network, which needs additional elements to function during crises and wars. Fortunately, the Czechs have thought of this, as stations and tunnels also have their own secret and restricted access areas, which contain technical networks, smaller storage and control rooms, and disinfection areas. The OSM tunnels are also connected to several other areas, such as the underground garages in central Prague, which are also equipped with blast doors.

In addition to OSM, there are 38 other larger STOU shelters in Prague, many of which are connected to OSM itself, such as the Strahov tunnel, which is not obvious at first glance, and that is how it should be. As a normal car tunnel (like the Peterburi maantee tunnel in Tallinn), which is part of a wider tunnel system running from the north to the south of Prague, it can be hermetically sealed on both sides with 40-ton doors in case of danger to create an additional shelter. There are also technical rooms and warehouses where an additional 15,000 people can take shelter (unlike the few mini-tunnels in Tallinn, which are to be built in the near future). As it is an integrated system, the Strahov tunnel is connected to the OSM network and the B line of the metro.

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Currently, all parts of the Prague OSM network and shelters can accommodate more than 450,000 people, but after the completion of two new metro lines (D and O), this number will reach 600,000.4-6

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