May 12, 1927 (Thursday)
- Under the direction of Scotland Yard, London police raided Arcost, Ltd., the office of the Soviet trade delegation. At 4:00 pm, telephone lines were cut and the building was sealed, with the 600 employees detained during a search. Evidence of Russian espionage was found and a break of diplomatic relations followed.
- Philip F. Labre applied for a patent for the "grounding receptacle and plug", the three pronged plug still in use today. U.S. Patent No. 1,672,067, was granted on June 5, 1928.
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