During the 1960s, one of the Polaris options examined by the United Kingdom was for a "mini Poseidon" which would have replaced the Polaris A3's three W58 Mark 2 RVs with six smaller W78 Mark 3 MIRVs used in the Poseidon SLBM. Ultimately, the "mini Poseidon" option was rejected in favor of the Chevaline penetration aids and decoys upgrade for the Royal Navy's Polaris SLBMs.
REFERENCES:
Jones, M. (2017). The Official History of the UK Strategic Nuclear Deterrent: Volume II: The Labour Government and the Polaris Programme, 1964-1970. Taylor & Francis.
Stoddart, K. (2012). Losing an Empire and Finding a Role: Britain, the USA, NATO and Nuclear Weapons, 1964-70. Springer.