If I recall correctly, the Duty Rumour of the time was that the Americans were sticking helicopter pilots into Harriers and thinking that they would be able to cope with kites that were flying a lot faster than they were used to, and many couldn't. According to the Wikipedia page, the RAF tried twice and it didn't work out - but thankfully there's no mention of the pilots stacking the planes into the ulu.
" On two occasions the Royal Air Force explored whether experienced helicopter pilots, with their ability to hover and transition to forward flight, would be a better source for Harrier squadrons. In both cases the pilots were completely out of their depth with conventional flight, navigation, orientation and weapons delivery at the high speeds of a fast jet."
Fast Jet mafia defend their Fast Jet mafia.
The RN (and RM) fairly often transitioned RW pilots into FW pilots. Indeed there was a specific course to do so.