The Atlantic 21 is part of the B class of lifeboats that served the shores of the United Kingdom and Ireland as part of the Royal National Lifeboat Institution (RNLI) inshore fleet. The Atlantic 21 was the first generation rigid inflatable boat (RIB), originated at and by Atlantic College in South Wales, the birthplace of the RIB after which the craft is so named. The school was also one of nine locations where the RNLI first established lifeboat stations using smaller inshore watercraft. Atlantic College Lifeboat Station was commissioned by the RNLI in 1963 and decommissioned in 2013.

The Royal National Lifeboat Institution (RNLI) is the largest of the lifeboat services operating around the coasts of the United Kingdom, the Republic of Ireland, the Channel Islands, and the Isle of Man, as well as on some inland waterways.