Apparently the RAF can only navigate when flying at multiples of 60 kts.
And there was me thinking that ground attacks were flown at 420 Kts from cab rank departure point to pull up point just to make it easy for us pongo FACs who had to work out how long it would take, as we huddled in a slit trench in the rain.
Or at least they were when it was Hunters from Chivenor.