In an attempt to reduce the vibration in a piston driven steam locomotive, the duplex drive, was invented. Two sets of driving wheels, driven by seperate pistons, were put into a single frame.

 

 

   Class Wheel Arrangement km/h hpi Year   
  
France: Nord
  
  600 CC n4t       1862
  
France: PLM
  
Info 75 -> 80
-> 151A		 1'BC1' h4v       1930
  
Germany
  
Info XV HT V
-> DRG 79		 CC h4vt       1916
  
Spain: Nord
  
  800 CC n4t          
  
USA: Baltimore & Ohio
  
Info N-1 2'BB2' h4       1932
  
USA: Pennsylvania Railroad
  
Info Q-1 2'CB2' h4       1942
Info Q-2 2'BC2' h4       1944
Info S-1 3'BB3' h4 193 km/h
(227 km/h)		 7200 hp 1939
Info T-1 2'BB2' h4 193 km/h
(220 km/h)		 6552 hp 1942
Info T-1a 2'BB2' h4 193 km/h
(220 km/h)		 6552 hp 1942