The TADEN was a British experimental light and medium machine gun firing the .280 in (7 mm) intermediate cartridge.
Alongside the bullpup EM-2 rifle design, it formed part of a proposal to reequip the British Army with new small arms which would use a round smaller than the .303 inch which was shown to be impractical for use in a modern assault rifle.
[1] The TADEN used the action and gas system of the Bren but fired from 250-round non-disintegrating metal-link belts rather than box magazines.
The TADEN and EM-2 projects were discontinued when the United States Army refused to consider the .280 cartridge for the new NATO standard on the basis that it was less powerful than their .30-06 Springfield round (and, as others have suggested,[2] the reluctance to adopt a round developed outside the USA).
It was decided that the TADEN and EM-2 could not realistically be reworked to take the new NATO round and alternatives were sought.