This week, the real action underground was played out after the last Metro had run its course. For, that was when commandos from the National Security Guards (NSG) would take over the Metro Railway stations to conduct ?top secret? security drills through the night.

The anti-terror training underground was matched by trials above. On Thursday afternoon, a state-of-the-art gadget to detect buried improvised explosives was tested at Alipore Police Grounds, in the presence of state home secretary Prasad Ranjan Roy and senior cops (picture on left by Amit Datta).

While the Metro Railway security drill coincided with the chief minister?s call on Wednesday for greater security underground, the purchase of four Ground Penetrating Radars is being considered to ?counter terrorist and Maoist attacks?, said a senior state police officer.

Each explosive detection device, manufactured by US-based Geo Physical Radars, will cost between Rs 70,000 and Rs 85,000. The trials, ?kept confidential?, were said to be successful.

The Metro Railway security drive, in collaboration with the special security unit of the Special Branch of Calcutta Police and some units of the detective department, was also conducted under wraps, so much so that even the local police stations were not aware of it.

?The NSG team is here for drills pertaining to security. It is a symbiotic process that enables both the commandos and our men to pick up valuable lessons on underground railway security. Since security policy matters are involved, it would not be proper to discuss the issue,? said Sudhir Mishra, joint commissioner (organisation) of Calcutta Police.

According to insiders, the commandos focussed on detection of explosives inside compartments and on the tracks, and dealing with explosions and other exigencies.

The team even worked on rescuing people in a hostage situation on a train. The commandos scanned the exit routes of the stations and chalked out evacuation plans.