There were only two classes of 4-8-4+4-8-4 steam locomotives worldwide, all of which were constructed by Beyer, Peacock & Company, the owners of the Garratt patent.

[1] The predecessor 4-8-2+2-8-4 Double Mountain was likely the optimal Garratt wheel arrangement, with the four-wheeled leading bogies and the two-wheeled trailing trucks on each engine unit ensuring stability at speed and with sixteen coupled wheels for traction.

More coupled wheels would inhibit the locomotive on tight curves, while the only advantage of more non-coupled wheels, such as on the Double Northern, was to reduce the axle loading.

The first 4-8-4+4-8-4s to be built were thirty class EC3 locomotives for the 1,000 mm (3 ft 3+3⁄8 in) metre gauge Kenya Uganda Railway (KUR).

These engines later became classes 57 and 58 on the East African Railways (EAR).