The Cletrac, the high speed 7 ton M2 tractor dozer

https://www.flickr.com/photos/oldbuckshots/8545525130/in/album-72157636999226295/

a "Cletrac," dozer tractor was used for moving aircraft and heavy trailers, particularly effective for moving vehicles or aircraft that had become bogged down in mud. The M2 had a gross weight of 13,800 lbs. and a maximum drawbar pull of 7,000 lbs.

 Also referred to as the "bomber nurse," since it contained a high-pressure air compressor, a 24-volt generator, a nitrogen bottle, a winch, and a center-mount drawbar for maximum traction that allowed it to tow B-17s around soggy English airfields with relative ease.

https://www.flickr.com/photos/133697406@N05/19276074851/

https://www.flickr.com/photos/133697406@N05/19246115116/

http://www.warbirdinformationexchange.org/phpBB3/viewtopic.php?p=479063

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