There was a few of them based at ISAF HQ back in 2008 - who I used to drink with, I'm pretty sure there were seven of them and they were all on first name terms from the colonel down to the lowly corporal.
The vertical grip is a bag of doo doo as far as ergonomics are concerned. You benefit more from having your hand at and angle as it presents a more natural position.
These chaps seem to have been to the Chris Costa (Costa Ludus) school of shooting, or someone who has adapted his teaching. That is an observation not only from the way the support hand is placed on the rifle but the way the pistol is presented into the 'personal workspace' for reloading and other manipultion.
In other news: I had a couple of days at Deland about 5 years ago with a bunch of Irish chaps who always seemed to be suffering terminal hangovers even after the first jump of the day. Good blokes.