This puzzle box that Elizabeth and Philip are fretting over is an enigma code breaking machine, and is probably pretty similar to a device used by the late Mavis Batey, one of Britain's only female code breakers during World War II. Batey died earlier this month at the age of 92, but her efforts at unscrambling the infamous German Enigma were critical in at least two major British successes in the war, including a naval victory at the Battle of Matapan in 1941.