 The 4-6-4+4-6-4 wheel arrangement is sometimes called a "Double Baltic" or "Double Hudson" Garratt.The Rhodesia Railways (RR) 15th class was one of only two Double Baltic Garratt classes built, the other class of "Double Baltics" being the Sudan Railways 250 class (which RR later bought and classified as their 17th class).The 15th class were largely based on the RR 16th class 2-8-2+2-8-2 Garratts.