What did RE 'HQ troops' do?

[mac657]

Gents, i 've been doing some research into my grandfathers RE service history during WW2 and he served mainly with Mechanical Equipment Units throughout his time. He also served with '4 HQ troops' within 21 army group, i'm led to believe that this was a 'pool' of heavy plant to be used when and where required on specialist tasks.This would fit with his trade of plant/crane op. I've had little luck finding out what RE 'HQ troops' actually did, although i have had a suggestion, does anybody have any idea?

Mac