From the current LRB letters page (the whole thing is fun, but this in particular caught my eye):
On 27 May 1940 an RAF bomber, aiming for a German airfield in Holland, flew into a magnetic storm which disabled the compass. Completely lost, the crew identified the Thames as the Rhine and bombed an airfield in Cambridgeshire.
I did not know this. Andrew Etherington’s website has more:
RAF Bomber Command: 4 Group (Whitley). Bombing – Dortmund, Duisburg, Dusseldorf and Cologne.
10 Sqn. Eleven aircraft. Ten bombed. One enemy aircraft claimed destroyed by tail gunner. One bombed Bassingbourn in error…
The 11th crew from 10 Sqn, failed to find their primary target and bombed what was thought to be an airfield in Holland. This was not the case. After carrying out their bomb-run they set course for home, but after flying for some time, and when the Dutch coast failed to show up, it was thought that something was amiss. This was confirmed when W/T bearings indicated that the aircraft was over England and flying on a westerly course. With the aid of further W/T assistance they were able to scramble back to base. A re-plot of the sortie was instigated and the unfortunate conclusion was reached that the airfield they had bombed must have been British! This was confirmed when communications with Air Ministry revealed that the RAF airfield at Bassingbourn, near Cambridge had been attacked at the same time the No. 10 Squadron crew presumed they were bombing an enemy airfield. Luckily there had been no casualties and only slight damage at Bassingbourn. Subsequently the story got around that one of the bombs had hit the W/T rest hut at the side of the airfield, passing through one wall, over the top of a sleeping airman and out the over side before exploding. The said airman then woke up!
Repercussions followed. The unfortunate skipper was demoted to second pilot and he and his crew subjected to much leg-pulling by the other crews. This included the dropping of a home-made ‘Iron Cross’ constructed from a tea-chest lid and some brown coloured cloth, by one of the other 4 Group squadrons. It was addressed to ‘Herr von (name withheld) from a grateful Führer.’
During subsequent investigation it was discovered that the magnetic compass had been rendered U/S when the aircraft had flown through an electrical storm after crossing the English Channel on its outbound flight.
It looks as if this would have been a bomber based at RAF Dishforth in Yorkshire.