Most Commonwealth realms and British overseas territories celebrate the Queen's Official Birthday in June. However, Saint Helena, Ascension and Tristan da Cuhna is an exception. Here the birthday of Queen Elizabeth II is observed on the third Monday in April which is close to its actual date.
World Amateur Radio Day is an annual observance held on April 18. It marks the anniversary of the establishment of the International Amateur Radio Union in 1925.
International Day for Monuments and Sites is an annual observance held on April 18. It was officially established by UNESCO in 1983, following the initiative of the International Council on Monuments and Sites (ICOMOS).