A Swedish 84 mm unguided, disposable, shoulder-fired anti-tank recoilless rifle built by Saab Bofors Dynamics. Technically it is not considered a rocket launcher as the explosive warhead is not propelled by a rocket motor, and the weapon itself has rifled barrel. Also known as M136 in US Army service.
The name AT4 is a word play on the 84 mm caliber of the weapon. 'Eighty four' being a homophone of 'A-T-4'. The name also doubles as an alpha-phonetic word play on the weapon's role due to "AT" being a common military abbreviation for "Anti-Tank".
This tag implicates rocket_launcher (learn more).