During the 20th century, roller skating also developed as a competitive sport. Roller-skating races were professional from an early stage. Professional World Championships were arranged in North America between the competitors on that circuit. Later, roller derby leagues appeared, a professional contact sport that originally was a form of racing. FIRS World Championships of inline speed skating go back to the 1980s, but many world champions, such as Derek Parra and Chad Hedrick, have switched to ice in order to win Olympic medals.
Like roller skating, ice speed skating was also professional in North America. Oscar Mathisen, five-time ISU world champion and three-time European champion, renounced his amateur status in 1916 and travelled to America, where he won many races but was beaten by Bobby McLean of Chicago, four-time American champion, in one of the races. Chicago was a centre of ice speed skating in America; the Chicago Tribune sponsored a competition called the Silver Skates from 1912 to 2014.
The New York City Police Department quickly responded with the Emergency Service Units (ESU) and other responders after the crash of American Airlines Flight 11 into the North Tower. The NYPD set up its incident command center at Church Street and Vesey Street, on the opposite side of the World Trade Center from where the FDNY was commanding its operations. NYPD helicopters were soon at the scene, reporting on the status of the burning buildings. When the buildings collapsed, 23 NYPD officers were killed, along with 37 Port Authority Police Department officers. The NYPD helped facilitate the evacuation of civilians out of Lower Manhattan, including approximately 5,000 civilians evacuated by the Harbor Unit to Staten Island and to New Jersey. In ensuing days, the police department worked alternating 12-hour shifts to help in the rescue and recovery efforts.
The search and rescue effort in the immediate aftermath at the World Trade Center site involved ironworkers, structural engineers, heavy machinery operators, asbestos workers, boilermakers, carpenters, cement masons, construction managers, electricians, insulation workers, machinists, plumbers and pipefitters, riggers, sheet metal workers, steelworkers, truckers and teamsters, American Red Cross volunteers, and many others. Lower Manhattan, south of 14th Street, was off-limits, except for rescue and recovery workers. There were also about 400 working dogs, the largest deployment of dogs in the nation's history.
Elements of the New York Army National Guard's 1-101st Cavalry (Staten Island), 258th Field Artillery, and 69th Infantry Regiment based in Manhattan were the first military force to secure Ground Zero on September 11th. The 69th Infantry's armory on Lexington Avenue became the Family Information Center to assist persons in locating missing family members.
The National Guard supplemented the NYPD and FDNY, with 2,250 guard members on the scene by the next morning. Eventually thousands of New York Army and Air National Guardsmen participated in the rescue/recovery efforts. They conducted site security at the WTC, and at other locations. They provided the NYPD with support for traffic control, and they participated directly in recovery operations providing manpower in the form of "bucket brigades" sorting through the debris by hand.
Additionally service members provided security at a variety of location throughout the city and New York State to deter further attacks and reassure the public.
Members of the Air National Guard's 109th Airlift Wing out of Scotia, and Syracuse's 174th Fighter Wing immediately responded to New York City, setting up camp at places such as Fort Hamilton. Mostly civil engineers, firefighters and military police, they greatly aided in the clean-up effort. F-16s from the 174th Fighter Wing also ramped up their flying sorties and patrolled the skies.
The New Jersey National Guard assisted the New York National Guard's efforts following the attacks.