Declassify Mission: Start with no ammunition for boltoks and longshots.
At the start of the mission, look to the left to find a COG tag skull. Check the corner past it to find the section's COG tag.
Activate the declassify mission skull if you want. There's a cleaver from the corpse beside where you got the COG tag earlier so you may want to get that. Cross the makeshift bridge and defeat the cleavers coming your way. There are snub pistols and stim gas inside so pick them up and kick the next door open.
Clear the water tower and rush towards it. Here, you'll find loads of ammo and some heavy weapons. Use this to destroy the enemy position ahead.
After clearing the enemies past the water tower, replenish your ammo or exchange them then continue forth to the door to complete the section.