Dive summary:

• What the Caterpillar 336E-H hydraulic-hybrid crawler excavator delivers is 50% more tons moved per gallon of fuel consumed than its predecessor, the 336D.
• In a development that yielded more than 300 patents, Caterpillar created a system that uses stores up pressurized fluid when the shovel swings one and uses that pressure to aid the swing back the other way and take strain off the diesel engine.
• The shovel, which will go on sale in February, is 25% more fuel efficient on a straight consumption basis than the non-hybrid version and 33% more efficient than the 336D.

From the article:

Seeking to deliver greater fuel efficiency in its line of earthmoving machines, Caterpillar Inc. has unveiled its first hybrid excavator, the 336E-H. ...