In the 1401's heyday, in the 1960s, some 9300 units were in use. Together with 6000-odd units of various successor models, by 1967 the 1400 line accounted for half of all the computers in the world.
The 1401 was a decimal arithmetic machine, designed expressly for business applications. It preceded the unifying System/360 line (all apps, commercial and scientific) by about five years.