Does anybody know if the route between Luton Rail Station and Hendon Station is overground?

The First Capital Connect route between Hendon and Luton Airport Parkway is primarily above ground, as far as I can remember there are no tunnels between those two stations, the only part of that line that is primarily underground is the central London part from Blackfriars to past St Pancras northbound (known to regulars as Thameslink).