Return through the crawlspace near the MJ-12 box. Drop into the water.

Swim through the white tunnel to the small room with the laser trap and climb out of the water.

Jump over the lasers, drop into the water....

...and follow the long, flooded tunnel...

...back to the pool below the SATELLITE DISH TOWER. Surface for air if you need it. Then swim down to the far left corner of the pool and follow the other underwater passage to the dark crawlspace.

If you took the shortcut earlier, or missed this pickup the first time, there's a small medi pack on the bottom of the tunnel just before you surface.

Go through the green crawlspace on the left into the hallway near the YELLOW LOCK ROOM.

Shoot the guard on patrol here and continue around the corner...

...to the ladder opposite a metal grate. Climb up.

NOTE: If you neglected to open the door here earlier and your way is blocked, return to the pool. Climb out of the water on the small, square ledge and jump clockwise around the edge of the pool to the green crawlspace. (This is covered in an earlier series of screenshots.) Follow the crawlspace, then the passageway beyond it, to the switch that opens the door on the other side of the grate. Return to the pool, swim down through the tunnel in the corner, and go through the dark crawlspace back to the hallway where you killed the guard. Now head to the right again and the door should be open.

Follow the ramp up to the square room at the base of the SATELLITE DISH TOWER. Go around or through the central structure to the other ladder. Climb up.

Then follow the yellow-and-white ramp up to the hallway where you got the SECOND YELLOW SECURITY PASS earlier.

Kill another guard and take the 2 pairs of grenades and KEYCARD TYPE B that he drops. Use the card in the card reader at the end of the hall to open the hatch there.

This is SECRET #2—the loaded GRENADE LAUNCHER.

[Return to the High Security Compound Walkthrough]