Union Railway Minister Piyush Goyal announced on Thursday that the first underwater will be operational under Kolkata's Hooghly River. He posted a video about the upcoming metro line on Twitter.

He tweeted, "The first underwater train will be operational under Kolkota's Hooghly River. After the metro train is operational, the residents of Kolkata will better facility and the country will be proud of it."

भारत की पहली अंडर वॉटर ट्रेन शीघ्र ही कोलकाता में हुगली नदी के नीचे चलना आरंभ होगी। उत्कृष्ट इंजीनियरिंग का उदाहरण यह ट्रेन देश में निरंतर हो रही रेलवे की प्रगति का प्रतीक है।

इसके बनने से कोलकाता निवासियों को सुविधा, और देश को गर्व का अनुभव होगा। pic.twitter.com/MDzj42s5XZ

— Piyush Goyal (@PiyushGoyal) August 8, 2019

He said that the underwater train is an example of excellent engineering. The video released by the Indian Railways, mentions that there are 'four protective covers' to prevent water leakage in the tunnel. 

The underwater train will be part of Kolkata Metro Line 2, which is also known as the East-West Metro. The total length of the metro line is 16-km, which will be made operational in two phases. Later this month, the first phase between Salt lake Sector 5 to Salt Lake Stadium station will be made operational, which will span across 5km. The underwater train will connect Salt lake Sector 5 to Howrah Maidan station. 

The tunnels are 520 metres long and about 30 metres deep. The tunnel boring machines were brought from Germany in parts and assembled underground for the construction of the tunnels.