As soon as the United States and North Korean leaders reached the Capella Singapore for the summit, the motorcade commanders, Deputy Assistant Commissioner Sherrin Chua and Deputy Assistant Commissioner Evon Ng, started getting ready for the departure.
It was just a sign of the close attention to details the two police officers, who each led a 60-vehicle convoy for the delegations, brought to bear on the historic event.
That meant taking charge of planning and carrying out security protection for both leaders on the road, while also working closely with their American and North Korean security counterparts.
"We always have to... consider the possible scenarios to get the convoy ready in the fastest possible time. So as soon as they reach their destination, we're already planning for their departure," said DAC Chua, 41. The deputy director at the police's planning and organisation department led the convoy for US President Donald Trump.
DAC Ng, 45, who led the motorcade for North Korean leader Kim Jong Un, added: "Our focus was to ensure the principals (Mr Trump and Mr Kim) reached each destination safely, securely and on time.
"Throughout the journey, we had to keep watch on all fronts and also report back to the command post to keep them informed about what was happening within the convoy," said DAC Ng, who is deputy commander of the police's public transport security command.
DAC Ng said each motorcade was made up of four "waves", with the first three ensuring the roads were clear of debris and pedestrians.
Then came the fourth wave - the main convoy - made up of about 40 vehicles and led by a traffic police officer on a motorbike.
The motorcade commander would be in the main convoy's second car to ensure that vehicles were coordinated and stayed close together. While each journey did not last more than 20 minutes as the roads had been cleared, preparations took at least two hours.
One factor considered was the length of the limousines for the leaders. "We needed to make sure the pace we went at facilitated the long convoy movements," said DAC Ng.
She also faced a language barrier with the North Koreans.
"To put a point across would take two conversations - between me and the interpreter, and the interpreter with the counterpart, and vice versa."
DAC Ng was a bit apprehensive during the first meeting with the North Korean head of security as she was unsure about how he would take to a female officer leading Mr Kim's motorcade security.
"(But) he listened to me very attentively. I was able to clearly convey to him our plans and I believe I got his trust."