On May 11, 1998, the Prime Minister of India, Atal Bihari Vajpayee, called a press conference. He was going to share something that was certain to leave the world stunned. 

Standing on the podium, the 72-year-old PM read a statement that forever altered India's image of a harmless democracy. He said.

I have a brief announcement to make. Today, at 1545 hours, India conducted 3 underground nuclear tests in the Pokharan range. These tests conducted today were with a fission device, a low-yield device, and a thermonuclear device. The measured yields are in line with expected values. Measurements have also confirmed that there was no release of radioactivity into the atmosphere. These were contained explosions like in the experiment conducted in May 1974. I warmly congratulate the scientists and engineers who have carried out the successful tests. Thank you very much indeed.
Source: YouTube

In the May of 1998, India had conducted 5 nuclear tests in the span of 3 days. 

A great success for India, it was to go down in history as one of the biggest intelligence failures of CIA.

The preparation of India's pursuit to becoming a nuclear power goes back to March 20th, 1998, when the newly-elected PM of India called Department of Atomic Energy chairman R. Chidambaram and DRDO head A.P.J. Abdul Kalam to his office and gave them a green signal to conduct the tests.    

Source: dnaindia.com

The mission was named Operation Shakti and the Indian army played a decisive role in its successful execution. 

On May 1st, nuclear devices were flown from BARC (Bhabha Atomic Research Centre) complex in Mumbai to Jaisalmer airport in Rajasthan from where 4 army trucks transported the devices and other equipment to a small city called Pokhran. 

Source: defenceforumindia.com

The 58th Engineers Regiment of the Indian army was assigned the task of maintaining the shafts in which nuclear devices, 6 in total, would be tested. 

The commander of 58th Engineer's Regiment, Colonel Gopal Kaushik, supervised the preparations and all the officers were ordered to maintain absolute secrecy. 

After digging the shafts, the army would return all the equipment used at night to their original place to give an impression to the ever-prying satellites that they were never moved. 

Source: nuclearweaponarchive.org

Around 80 scientists from BARC and DRDO, who were involved in the operation, were required to wear army uniforms and most of the work was conducted at night. 

Even the DRDO head A.P.J. Abdul Kalam and Chidambaram would wear army greens during their visit to Pokhran.

Source: thequint.com

While the shafts were being dug, the engineers would place a fence around them to keep the stray cattle and locals away.

To prevent the satellites from capturing any undisclosed activity, they would put up signs such as 'Danger. Mined Area. Keep Out,' 'Water Position' and 'Dozer Cadre Training'.

To avoid the huge mounds of sands, which were used to seal the shafts once the nuclear devices were placed inside them, from being captured by the satellites, the army examined how winds shaped the mounds and would align them in the same direction.

Source: Outlook

For the first round of tests, the shafts were given code names such as White House, Taj Mahal and Kubhakaran. 

The other three shafts for the second test series were named as NT 1, 2, and 3.

On May 11th, India finally conducted 3 underground nuclear tests in the shafts named White House, Taj Mahal and Kubhakaran and Prime Minister Atal Bihari Vajpayee announced it in an official statement.

Source: SpokespersonMOD/Twitter

Just as it was expected, there was a huge outcry against India in the international community. The then US President Bill Clinton was "deeply disappointed" and termed the tests as "unjustified". 

The international community also blamed India for breaking an informal moratorium on nuclear testing that went into effect in 1996.

Nevertheless, undeterred by the criticism of so many nations, India went ahead and conducted two more tests on May 13th. Even though the move invited economic sanctions from the US and Japan, Indian citizens were elated and openheartedly welcomed the tests.

Source: zeenews.india.com

As the noted journalist and Swapan Dasgupta rightly said, after India had asserted itself as a nuclear power on the world map, the operation was more of an emotional event for the whole country.

To Indians, it is evidence we count, that there is nothing to fear but fear itself. Pokhran is only tangentially about security. Its significance is emotional. The target isn't China and Pakistan. It is the soul of India...The mood is euphoric. Not the time for aesthete contrarians to embrace treachery.

And that's how India created history!