The assassination of President John F. Kennedy in 1963 forever changed the U.S. Secret Service and how it protects American presidents.
The tragedy prompted a top-to-bottom review of the agency's protocols, triggering a sweeping overhaul of its advance work and protective details. Immediately out: the use of open-top limousines. Immediately in: better radio technology and more agents by the president's side at all times.
"After the Warren Commission investigation of the assassination of President Kennedy, significant changes took place in the Secret Service," Deputy Director A.T. Smith told ABC News.
The Secret Service also developed and deployed new counter-sniper and counter-assault strategies. And Congress began giving agents expanded powers, like the ability to make arrests without warrants, something they never had.
The changes have continued in the 50 years since JFK as technology and threats to the president have evolved. "We've grown from a domestic law enforcement agency to a global law enforcement agency," Smith said. There have been five direct assaults on presidents, but all failed.
ABC News visited Secret Service headquarters this week for a closer look at the agency's protective mission and how it's matured over the last five decades. Here are five ways the JFK assassination changed the Secret Service:
1. More Money & Manpower
When President Kennedy was shot, the Secret Service had just 350 agents on-duty nationwide with an annual operating budget of roughly $5 million. The hundred-year-old agency, formed by President Lincoln to combat counterfeiting, was still primarily in the business of criminal investigations. Its protective mission was robust, but often "inadequately defined," the Warren Commission later found.
Today, the ranks of the Secret Service have grown dramatically to more than 3,500 agents, with most of those dedicated to protection of the president and other dignitaries. Last year, the Service spent more than $1.6 billion on operations, including more than $1 billion on presidential protection alone.
2. Intelligence Gathering
Two years after JFK's assassination, the Secret Service created an intelligence division solely focused on collaborating with local law enforcement ahead of and during a president's visit. Critics had faulted the agency with not having clear and open lines of communication with local police in the cities presidents visited before 1963.
Today, anywhere the U.S. president goes, Secret Service partners closely in advance with law enforcement on the ground, building layers of security around event sites and chasing down every threat -- from physical to electronic -- that comes to light.
"It used to be that when someone made a serious threat against one of our protectees, normally they'd sit down and write out a letter... and if they were really nice, they'd put the return address on the envelope and we'd know right where to go to interview them," Smith said. "Today, we have to run to ground so many threats, with many coming over the internet."
3. Counter Sniper Units
In 1963, it was not common practice for the Secret Service to inspect buildings along a motorcade route for potential sniper nests. As the presidential limo drove along the motorcade route, there were no teams of agents scanning windows of buildings for shooters lurking inside.
Today, those activities are common practice. Countersniper teams are solely dedicated to preventing another attack like that by Lee Harvey Oswald, while counter-assault units are trained and prepared to combat other types of physical attack.
"The counter-sniper unit is a very integral part of that protective advance because no matter how hard we try to keep the president or the vice president under constant cover or in that limousine, there are going to be times when he's outside and he's exposed," Smith said.
4. Preparing for New Threats: Chemical, Biological, Radiological
While snipers and gunman remain significant threats, the Secret Service of 2013 is intensely focused on chemical, biological and radiological weapons and improvised explosive devices, officials say.
A technical security unit, formed in the wake of the Warren Commission, "takes a very proactive look at the security within an advance or within a visit of a president or vice president that could go wrong," Smith said.
Chemical and biological threats, like anthrax and ricin, are particularly concerning to the Secret Service because it only takes a very small amount of a substance to cause significant bodily harm, and possibly death.
5. Congress Grants Greater Powers, Responsibilities
In the 50 years since JFK's death, Congress has enacted more than 23 statutes aimed at strengthening the Secret Service and expanding its responsibilities for protecting top officials and their families.
In 1965, the Service began permanently protecting living former presidents, their spouses and young children. Three years later, protection was extended to some presidential candidates. By 1971, the mission was expanded to include visiting foreign heads of state and U.S. officials abroad on business.
White House grounds officially came under Secret Service purview in 1970, with protection of presidential and vice presidential residences expanding to out-of-state locations in 1976.
In the 1980s and '90s, Congress authorized the Service to take on new challenges of the electronic age, including investigations of credit card and computer fraud, missing and exploited children, and so-called "national special security events" that require extensive planning and coordination.