Frederick sometimes changed his line of operation in the middle of a
campaign; but he was enabled to do this, because he was manœuvring at
that time in the centre of Germany--an abundant country, capable of
supplying all the wants of his army in case his communications with
Prussia were intercepted.
Marshal Turenne, in the campaign of 1746, gave up his line of
communication to the allies in the same manner; but, like Frederick,
he was carrying on the war at this time in the centre of Germany, and
having fallen with his whole forces upon Rain, he took the precaution
of securing to himself a depôt upon which to establish his base of
operation.
By a series of manœuvres, marked alike by audacity and genius, he
subsequently compelled the imperial army to abandon its magazines, and
retire into Austria for winter quarters.
But these are examples which it appears to me should only be imitated
when we have taken full measure of the capacity of our adversary, and
above all, when we see no reason to apprehend an insurrection in the
country to which we transfer the theatre of war.