In 1829 the first modem police force, the London Metropolitan Police—aka “Bobbies”—developed the first standard police apparel—a dark blue, paramilitary-style uniform. The color blue was chosen to distinguish the police from the British military who wore red and white uniforms at the time. Following their lead, including the color choice, U.S. police departments began to institute dress codes. New York was the first in 1853.
Early uniforms consisted of a high-collared, tailed, dark navy wool coat with shiny buttons, and a top hat. The tails were soon removed, leaving a tunic style coat, and the top hat replaced with a custodian helmet (peaked top with a chinstrap). By the 1950s, the U.S. uniform included blue pants, blue shirt, and a flat cap with a visor on the front.
Today, each branch of law enforcement uses different uniforms and although they vary in styles, they are still used most effectively to attain the same purpose they did hundreds of years ago—to increase visibility and help officers perform their jobs.