Infantrymen were the foot soldiers armed with muskets or rifles and bayonets. It was upon the infantry that the strength of the other arms of the service was based. When the infantry volunteer companies were mustered into active service in 1861, their roles quite often designated companies as light infantry or riflemen. These terms were a carry-over from the years before the war when most infantrymen were armed with the smoothbore musket. The troops comprising the infantry were divided into heavy and light; these distinctions arising partly from the kind of weapon they carried, and partly from their role on the battlefield. There were normally two companies of light infantry in a regiment of ten companies. The heavy infantry was known as the infantry of the line. The light infantry were charged with the responsibility of opening an engagement and covering the front and flanks of the infantry of the line. With the advent of the rifled musket, however, the distinction between the classes of infantrymen became nominal. After their muster into service in 1861, these terms all but disappeared.