Sub-Roman Britain (Cavalry etc)

[M. Demetrius]

Considering the centuries that Rome dominated the military system, it seems unlikely to me that people/soldiers would remember much of what had gone on before. There's a lot of generations in 400 years, however you measure it. Nobody living would have direct memory of the beforehand tactics, and it's not very likely that they'd have the ability to train the troops in the "old" ways. So maybe it's obvious that the soldiers would use the tactics and training (particularly if there were some Roman soldiers still living there) of the Romans of that day. The immigrants from non-Roman areas would, of course, bring their own styles and systems with them.