Á þriðja og fjórða áratug þessarar aldar urðu loftskeytasendingar á dulmáli um ferðir varðskipa, svokölluð „ömmuskeyti", nokkurt hitamál í íslenskri pólitík. Frá lokum síðari heimsstyrjaldar hefur lítið verið fjallað um þetta mál og það hefur ekki vakið verðskuldaða athygli sagnfræðinga. Hér er fjallað um helstu þætti „ömmumálsins."
Wirelesses were first installed in British trawlers just before the First World War. After the war most trawlers fishing off Iceland, British as well as Icelandic, were equipped with this new technology. Although the main purpose of the wireless was to ensure the safety of the trawlermen, skippers soon began using them to send coded messages concerning movements and whereabouts of Icelandic coast-guard-vessels. Icelandic skippers formed so-called //Code-societies", often with the participation of the trawler owners, while British trawlers received information from agents ashore. The sending of such messages was illegal, but until 1927 the only reaction of the Icelandic authorities was to build more coastguard-vessels in an attempt to make the patrolling of the fishery limit more effective. In 1927 a new government came to power and a bill was soon tabled on the control of wireless messages going to and from the trawlers. This was defeated, however, and it was not until 1936, when five people admitted to having sent illegal information on the movements of coast-guard-vessels, that the government finally decided on a provisory law permitting control of the use of the wireless. As a result, eight Icelanders were found guilty of „spying" on the coast-guard in 1937-38, and were made to pay heavy fines. The „granny-grams", as these illegal messages were generally called, because of the code allegedly used, were one of the mostly debated political issues in Iceland between the wars. Since e Second World War, however, the subject has seldom been discussed and has hitherto been paid little attention by historians.