Determining the subgroup structure of algebraic groups (over an algebraical
ly closed field K of arbitrary characteristic) often requires an understand
ing of those instances when a group Y and a closed subgroup G both act irre
ducibly on some module V, which is rational for G and Y. In this paper and
in Overgroups of irreducible linear groups, I(J. Algebra 181 (1996), 26-69)
, we give a classification of all such triples (G; Y; V) when G is a non-co
nnected algebraic group with simple identity component X, V is an irreducib
le G-module with restricted X-high weight(s), and Y is a simple algebraic g
roup of classical type over K sitting strictly between X and SL(V).