Intervention is not conquest: Britain and Russia

Was the British Army ever large enough to conquer Russia?

No; Britain could undertake limited operations or exploit a civil war, but that is very different from fielding an army able to take Russia.

A headline about the British Army being too small to fight Russia raises the distinction between national conquest and limited intervention. Britain has not fielded an army large enough to take Russia as a whole. It could seize limited areas or intervene during a Russian civil war, when the political and military problem would be very different. Army-size comparisons only make sense after the intended objective and the condition of the opposing state are defined.