MI6 agents used ‘bodily fluids’ as invisible ink

SERVING officers experimented with using semen as an invisible ink to write top-secret letters during the World War I, according to Keith Jeffery’s book.

MI6 agents used ‘bodily fluids’ as invisible ink

A senior officer found that the bodily fluid could act as an effective invisible ink which did not react to the main methods of detection. Better still, it had the advantage of being readily available.

But the plan fell apart with problems when correspondents failed to use fresh urine and an unusual smell was detected.

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