IIRC, early Halifaxes had problems with the rudder(s) locking over which was traced to the swept leading edge of the fin. Later ones had a much larger oblong fin and rudder.
Radlett was easy for me to remember - I passed it every week or two as a kid travelling to see both sets of grandparents. Despite now living in Derbyshire, I'm Hertfordshire born and bred.
For a small largely agricultural county that a lot of people have never heard of, with Hatfield, Radlett, Leavesden and Aldenham an awful lot of aircraft were produced there.