Wednesday was one of the biggest days in recent history for Londoners. The 2012 Olympics will be held under the colors of the Union Jack.
In a cruel twist, the day after the announcement became one of the country's darkest.
It could have been worse, says Texas A&M's homeland security expert.
"They clearly targeted the transportation sector," said David McIntyre, the director of the Integrative Center for Homeland Security. "This was not just about killing the most people. If it had been about killing people, they would have used yesterday as the target of opportunity. Instead, they attacked the transportation sector at a time when people are travelling."
In this day in age, the effects of acts like these are immediate and far-reaching. The US alert level for mass transit was elevated as a result. When it lowers is another question entirely.
"It's very hard because the longer you stay, the more expensive it is," McIntyre said, "and nobody wants to be the guy that steps back from Level Orange the day before an event takes place."
And no matter what the threat level, McIntyre says the strides in preparedness have been immense in the last three years. Take the hurricane evacuation drill in College Station last week as an example.
"The scenario would work just the same if they were having to leave Houston for some other reasons, some other type of attack," he said.
That's just the preparation. As Britons learned Thursday, as Americans learned in 2001, prevention is a whole different ballgame, and not one Olympians will compete in.
"We need to prepare ourselves psychologically for the fact that we can't defend everywhere against everything all the time," McIntyre said. "Sooner or later, we will get an attack that succeeds. We need to prepare, as a nation, to get up the next morning and go back to work."
As Londoners have learned, anything can happen the next morning.