Use the ant lions as a decoy. It was the hardest part of the game for me in the end I only <50 life. I think I went down to 43. To compare I never had lower than <70 life for the rest of the game. HL2 is actually incredibly easy. There is one big crate (doing this by memory here) close to the Rocket casket right before you advance to the next portion of the level. Use that crate as a shield. When you shoot your rocket the gunship should try to shoot it down so it will distract the gunship from focusing on you right there. Don't just shoot the rocket in a straight line manuever it. The gunship will not fire on you when its distracted. Use the ant lions as decoys when moving place to place. Watch out for the combine is a tower ahead of the Rocket crate. Just fire a rocket at them when you get the rocket crate. Don't try to finish both gunships at the same time. I never waste any rockets so I had a full load once I got to that area. Fired three at the first gunship and then there should be more rockets lying around. Finished first gunship before climbing stairs to the rocket crate where I finished the second gunship. The dumb combine made me lose more life than the gunships. Especially the one I mentioned. I had 100 life before climbing the stairs.