Our enemies there are fortified with earthworks and they have cannon.

If they hold the place they are likely to increase heavily in numbers.

It is our business to drive them out." The colonel told some of the officers within Harry's hearing that they could attack before dawn, but night assaults, unless with veteran troops, generally defeated themselves through confusion and uncertainty.
Nevertheless, he hoped to surprise the Northern soldiers over their coffee.

For that reason the men were compelled to lie down in their blankets in the dark.

Not a single light was permitted, but they were allowed to eat some cold food, which they brought in their knapsacks.
Although it was June, the night was chill on the high hills, and Harry and his two friends, after their duties were done, wrapped their blankets closely around themselves as they sat on the ground, with their backs against a big tree.