Uckers is a two-or four-player board game traditionally played in the Royal Navy and has spread to many of the other arms of the UK Armed Forces as well as Commonwealth Forces. It can now be found also in the Royal Marines, Army Air Corps, Royal Canadian Navy, Royal New Zealand Navy, Royal Australian Navy, Royal Australian Air Force (RAAF), Royal Dutch Navy, and the Royal Air Force (RAF).
It is believed to originate in the 18th/19th centuries from the Indian game Pachisi, although the first reference to it in print does not appear until 1946. It is mentioned in a diary by EJF Records (served 1928-1950) in 1937 as Huckers. Uckers is generally played using the rules stated here, which are the rules the app follows but these will vary from one branch of the Royal Navy to another, most famously with the WAFU Rules of the Fleet Air Arm.
Where those branches of the RN have worked with the other Armed Forces this usually has dictated what rules the new playing Service use; why fellow aviators tend to play under WAFU Rules for example.