This verse is one long sentence in Revised Standard Version, but it is divided into two by Good News Translation. Most translators will find Good News Translation better.

As soon as it was dawn may be rendered “When the sun rose the next day” or “Early the next morning” (Contemporary English Version).

They went out in companies to the passes in the mountains: In companies mean they went out in battle formation to make the Assyrians think they are about to attack. Went out … to the passes in the mountains sounds like they went trekking off somewhere. They didn’t go anywhere but outside the walls. The town is on an elevation, so that when the soldiers are outside the walls, they are already at “the slopes in front of the town” (Good News Translation). They will go down, of course, but not until 15.3. This action is a tactical trick. It is a pause to give the Assyrians time to become disorganized.

An alternative translation model for this verse is:

• When the sun rose the next day, the Israelites hung the head of Holofernes on the town wall. Then they took their weapons and went out of the town in groups, and stood on the side of the hill just below Bethulia.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Judith. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here.