A walkthrough for Call of Duty : Black Ops – Crash Site
by Kenneth Stubbs (OmegaMustard)

Crash Site
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You start in a military camp.  Make your way to the boat but right before
you get to the dock.

Intel – Grab the intel on the left table before the dock.

Get on the boat and start heading down river.  Once you get a bit down the
river, start shooting at the trucks and houses.  You have a machine gun and
rockets you can fire.  Take out the two trucks on the left side mountain. 
Continue to the dead end and shoot the huts and people running up on the
cliff. Now turn around and head back the the way you came.  You will see
a bunch of helicopters destroy a dam.  Now head that way.  As soon as you
get past the destroyed dam, shoot a rocket at the search tower and hose
down the huts with your machine gun.  Take it slow if playing on veteran
because it only take two sometimes one rocket to kill you.  Take out the
tower in the distance.  You will now be prompted to kill a truck on the
right. Continue on, going slow and blowing through the huts.  Take out the
two towers in the far back and you will be prompted to take out another
truck on the right side. Make your way down a bit and start shooting the
huts on the left. Quickly kill all the ground troops because a few are
carrying rocket launchers. As you progress past these huts, two boats
will come out in front of you plus a search tower on the right cliff.
Shoot the boats with your MG turret and fire a rocket at the tower on
the right side.  Make your way around the left bend and take out the huts
on both sides and then shoot the two towers it prompts you to destroy.
When you get closer to the big open water, you will be attacked by a
huge boat.  Keep your MG turret on it and wait for it to get close and
then eat it up with rockets.  Try to stay back a bit because there are
some enemies shooting rockets on the hillsides around the open water.
After you take out the boss boat, you will black out and come to in
front of a burning hut.  Just follow the river up marker to marker until
you dock.  As soon as you exit the boat a few steps on the path.

Intel – Intel will be on the right side of the path.

Make your way up the path a bit and you will see a flare fly up in the air.
You will then be attacked by three guys running at you.  Take them out and
take cover behind a rock looking to the right.  Pick off the soldiers hiding
in the trees and running out of the jungle.  Once you have cleared them out,
make your way up and you will be attacked by more soldiers.  Bowman will
yell sniper in the tree so make sure you take him out first.  Now clean up
the enemies that are hiding in the trees underneath the sniper you just
killed. Continue following your team slowly up the river.  You will see your
helicopters get taken down.  Take out the guys that run at you and continue
down the river.  Bowman will yell about another sniper in the tree on
the right so take him out quick.  Make your way up and you will come to
what looks like a blown down fence.  Stay at the top of the hill and take
out all the soldiers that run out the jungle from here.  Once it is clear,
fall down the hill and head left. A sniper will be in the tall tree on the
right.  Shoot him and start take out the guys that run up and hide behind
the blown down fence pieces.  Once you have killed them all, your
character will say thats all of them and you will continue up.  Climb up
the wing of the plane and fall down on the right. 

Intel – Look on the edge in front of you for this piece of intel

Now fall down again. Go inside the plane.  You will hear Woods and Bowman
talk a bit about Nova 6.  Pick up the Dragonuv sniper rifle and then make
your way to the cockpit.  Snipe the enemies on the ground until the boats
come.  Sniper the two people on both the boats and then Woods will say the
helicopters are back.  This will prompt a cutscene.  Afterwards the level
will end.

Source :The Call Of Duty Black Ops Walktrough FAQ