Redouble
Redouble (r?*d?b"'l) , transitive verb
[Prefix re- + double: compare French redoubler. Compare Reduplicate.]
To double again or repeatedly; to increase by continued or repeated additions; to augment greatly; to multiply.
So they
Doubly redoubled strokes upon the foe.
Redouble , intransitive verb
To become greatly or repeatedly increased; to be multiplied; to be greatly augmented; as, the noise redoubles.