billovitch,
RAF Compass swings were much more accurately done than civilian swings. Military aircraft must be able to get about without reference to ground based aids. In a war situation your enemy is not likely to leave the VORs operating or provide ATC to help you find your way
Before INS most RAF aircraft carried a navigator and used doppler updated Ground Position Indicator Systems to track the aircraft's position. The Doppler needed really accurate compass data and it was not unusual to spend a whole day swinging the compasses to get them accurate within a quarter of a degree. So, a lightning strike would be quite capable of putting the compasses out of calibration. When I got rid of my Blue Serge Suit, I was a bit taken aback by the casual civilian approach to compass swings, but IRS has sent the things to the museum now. Standby compasses are mostly only accurate to the nearest 3 or 4 degrees these days.
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Through difficulties to the cinema