Sentence:  In all three tunnels the full face was drilled at once. ... [T]he mucking machine was immediately converted into a drilling <WSD>jumbo</WSD> upon completion of the mucking operation. Both <WSD>jumbos</WSD> carried all the posts and bars necessary for the mounting in any desired position of four automatic DA-30 drifters. 
Meaning of the word marked with <WSD> tags:  A platform-mounted machine for drilling rock.