An MD-3A tow/starter tractor, used on aircraft carriers for moving aircraft and getting them started

if I understand what I heard, that big attached section on the back is a small jet engine,  a Gas Turbine Unit (GTU) that would be used to provide Bleed-Air to jet aircraft so as to start their engines. They saw service aboard US Navy Carriers from the early 1960's until the early 1990's,  designed primarily for use with jet powered aircraft that didn't have their own APU, such as A-7's, A-4's, F-4's F-14's etc

 

https://nara.getarchive.net/media/a-flight-deck-crewman-uses-an-md-3a-starting-tractor-to-start-an-aircraft-engine-6f52fa

https://steamcommunity.com/sharedfiles/filedetails/?id=2318656173