Minutemen

Although the terms militia and minutemen are sometimes used interchangeably today, in the 18th century there was a decided difference between the two. Militia were men in arms formed to protect their towns from foreign invasion and ravages of war. Minutemen were a small hand-picked elite force which were required to be highly mobile and able to assemble quickly. Minutemen were selected from militia muster rolls by their commanding officers. Typically 25 years of age or younger, they were chosen for their enthusiasm, reliability, and physical strength. Usually about one quarter of the militia served as Minutemen, performing additional duties as such. The Minutemen were the first armed militia to arrive or await a battle.

...Thus, although lacking central command, the Minutemen were still better organized and battle-tested than any other part-time military. They were a vital and necessary force, playing a crucial role in not only the Revolutionary War, but in earlier conflicts. Without these "ready in a minute" men, our history may have been written in a very different way.

From ushistory.org