Did Nelson's assisted loading anticipate Vanguard?

Was Nelson's assisted-loading arrangement similar to the system later seen in Vanguard?

To an extent, yes, although both are better understood as mechanically assisted systems than as complete autoloaders.

A viewer compares Nelson's assisted loading with the later arrangement in Vanguard. The systems share some continuity as part of the wider British effort to mechanize the heavy work inside a capital-gun turret. Extensive powered assistance still stops short of automating ammunition selection and the complete loading cycle.