400 class or Class 400 may refer to:
FS Class 400, 0-8-0 steam locomotives GS&WR Class 400, 4-6-0 steam locomotives New South Wales 400/500 class railmotor NS Class 400, diesel locomotives South Australian Railways 400 class, 4-8-2+2-8-4 steam locomotives South Australian Railways Redhen railcar#400 class double-ended power cars