It is generally thought is bailed out of her plane successfully, but drowned.
Although she was seen alive in the water, a rescue attempt failed and her body was never recovered. The incident also led to the death of her would-be rescuer, Lieutenant Commander Walter Fletcher of HMS Hazlemere, who dove into the chilly winter waters for Johnson.
The searchers did find her flight authorization papers and some gear
bearing her name.
The mysterious circumstance of how she came to be so far off course and her disappearance under the waves has lead to various theories. One maintains that she was flying a spy mission and was shot down by either friendly or enemy fire, while another speculates that she staged her own death.
But reports from two men associated with the Haslemere offer two different, but feasible, scenarios. From statements given for Probate Court proceedings soon after her disappearance, one Haslemere seaman said Johnson drifted to close to the ship's stern and the heaving seas brought the ship down on top of her. And more recently, during a BBC interview, a wartime clerk at the RAF flight office at Sheerness says that he prepared a report for 5 January 1941 for another of the ship's seaman. In it the seaman claims that because Johnson was unable to reach the ropes tossed to her, someone threw the engines in reverse and accidentally drew her into the propeller.
She was the first member of the British Air Transport Auxiliary to die in service.
Her commanding officer Pauline Gower, who headed the women's section of the ATA, defended Johnson's record saying that the aviator would never had done anything reckless or unwise.
Her death in an Oxford was somewhat ironic, as she had been one of the original subscribers to the share offer for Airspeed, the plane's manufacturer.