The loss of Hermes G-ALDN in the Sahara in 1952, which was mis-navigated and flew the wrong heading for several hours, was brought about by no navigator being available at Tripoli on crew slip, and a standby FO being assigned who didn't understand the instruments fully.
The Accident Report makes interesting reading.
http://fer3.com/arc/imgx/G-ALDN-26-May-1952-report.pdf
The navigator had mis-set an instrument because the graduations were in tens of degrees and he thought they were single degrees, and when a star didn't fit the expected plot it was disregarded, resulting in a 60 degree drift.