https://en.wikipedia.org/wiki/Bilberry

"Often associated with improvement of night vision, bilberries are mentioned in a popular story of World War II RAF pilots consuming bilberry jam to sharpen vision for night missions. A study in 2000^[6] by the U.S. Navy found no such effect and origins of the RAF story cannot be found.^[7] After the introduction of radar, RAF bombing became more accurately targeted, but to confuse the enemy, the story was leaked that it "was something in the pilots' diet" that improved their targeting - that something was carrots, not bilberries, and the story was concocted merely to keep the Germans from knowing the real reason for improved accuracy."

http://www.webmd.com/vitamins-supplements/ingredientmono-202-BILBER...

Bilberry is used for improving eyesight, including night vision. In fact, during World War II, British pilots in the Royal Air Force ate bilberry jam to improve their night vision, but later research showed it probably didn’t help. Bilberry is also used for treating eye conditions such as cataracts and disorders of the retina. There is some evidence that bilberry may help retinal disorders.