The Red Defence Force (RDF) was an independent group that included members of, but was distinct from, the International Marxist Group (IMG) and IMG-related 'Spartacus League'.
There are a handful of reports suggesting that this was an unarmed combat wing used by the groups above during demonstrations and that some related training had previously taken place.
However, if this was the purpose of the group, the evidence is that the RDF's tactics were ever put into action at any demonstration. Piers Corbyn, who was mentioned as a member of the organisation, instead suggested it was formed to protect the Notting Hill community against aggressive policing and called into question the accuracy of SDS officer HN338's reporting on the group.
Source: T1P2 Evidence Hearing.