Waukesha Engine recently held a somewhat unusual homecoming event marking the return of one of its Enginator generator sets. But this was no ordinary gen-set. This particular unit had literally been to hell and back, as it was one of six emergency gen-sets installed in the World Trade Center.

Originally five Waukesha V12 diesel generating units, each rated at 1200 kW, were installed during the construction of the WTC. Later, a sixth unit was added. The engine/generator units were located in subbasement 6, the lowest level, on the west side of Tower One.

In 1993, a bomb planted by terrorists exploded in the underground garage of the north tower. During that event, the gen-sets ran for 3 hours, 10 seconds, when water levels from broken piping forced their shutdown.

On September 11, 2001, the twin towers and 7 World Trade Center collapsed in a terrorist attack when two commercial jetliners were crashed into them. Nearly 4000 people, including fire and rescue workers, were killed. It is believed the engines came on-line to supply emergency power for a brief period, as in some early videos the lights were on in parts of the building and complex even as the towers started to come down.

The World Trade Center Enginators were sold by Kraft Power. The original engines, L5792DSIs, powered Kato generators and were shipped in August of 1971. A new Enginator was shipped in December 1984 and a replacement engine was shipped in January 1989.

"History is marked by important, life altering events that are remembered as infamy," said Waukesha President Bill O'Connor in comments to employees gathered outside the Waukesha, Wis., manufacturing facility "Today is a homecoming. It is a homecoming for an important piece of machinery.

"The six units were believed to have begun providing emergency power, as they were programmed to do immediately following the crashes. These engines supplied the power that helped light the stairwells that brought thousands out of the building before it collapsed, and allowed fire and police departments to search and rescue," O'Connor said.

Of the six engines, three were declared unsalvageable and immediately scrapped. Two are being rebuilt for other productive service, with the third returned to Waukesha.