An emergency response unit is a name for a law enforcement or other civil government entity that is trained and equipped to respond quickly to emergency situations.
In some instances, it can be a designation given to a special weapons and tactics unit, although it can also be used for units intended to respond to natural disasters and other situations not requiring the use of weaponry.https://pmc.ncbi.nlm.nih.gov/articles/PMC7786858/
Units Below are examples of units that use the ERU moniker:
Garda Emergency Response Unit, a specialist armed tactical intervention team of Ireland's police Emergency Response Unit (IFRC), pre-trained teams of specialist volunteers of the International Federation of Red Cross and Red Crescent Societies Emergency Response Unit (Cyprus), a division within the Cyprus police Emergency Response Unit (Liberia) London Underground emergency response unit
References
fr:Emergency Response Unit