keep your powder dry be ready for action; remain alert for a possible emergency.
☞ When his troops were about to cross a river, the English statesman and general Oliver Cromwell (1599–1658) is said to have exhorted them: 'Put your trust in God; but mind to keep your powder dry'. The powder referred to is gunpowder.
2005Daily Telegraph The suicide bombers seem to be less active than usual-but that may just be because they are keeping their powder dry for a post-constitution blitz.