You can take advantage of the arrangement of the warehouse platforms in this stage to avoid a majority of the enemies. Always climb up the ladders to the highest platform, and jump from the upper platform to the next middle platform beyond. Some of the gunners will follow you, along with the occasional rocket launcher equipped soldier, but for the most part, you will avoid a lot of confrontation. There are three supply runners in this portion of the stage, which all give grenades. Try to snag the grenades from the first supply runner, and use them against the third supply runner. When you land on the platform where the third supply runner was waiting, immediately throw another grenade to take out the grenade launchers on the ground below. Be prepared to jump out of the way when the first grenade launcher fires at you. Once you get past the grenade launchers, be prepared for a string of combat specialists. Jump into the air and take them out as they approach. You will reach the first forest wall. There are sets of grenade throwers on the top. Stay on the bottom and let them come to you (watch out for more combat specialists on the ground.) Climb up the second ladder after you remove the grenade throwers to confront the next supply runner who has a rocket launcher which you will definitely want to hang on to.
When you clear the first forest wall, a parachute soldier will drop down from the sky, and land mines will line the floor. A safe strategy is to climb down the last ladder of the forest wall, crouch down and shoot a rocket. You will take out at least two mine, a slew of foot soldiers, and run safely beneath the parachute soldier. Do this every time a land mine comes into view, and you will reach the next forest wall. It is actually rather short and leads to a cement wall. Along the floor in front of the wall, you will encounter grenade launchers, land mines, and combat specialists. If you've held on to at least on more rocket launcher, crouch down and fire so that you take out the land mines and the grenade launchers. Soon thereafter, you will encounter a supply runner in front of a grenade launcher. Take care when approaching him, as there is a combat specialist just waiting to rush you and jump kick you as you attempt to get the supply runner's weapon. Lure the combat specialist out first, then clear the area before going for the supply runners weapon. You can use his grenades to clear out the remaining enemies until you reach the end of the stage.
After you pass the penitentiary where the POWs are held, you will reach a solid brick wall. The alarm will sound and the area will clear out. Three soldiers in special heat gear will show up, one at a time, with flame throwers. Their flame throwers act just like yours do, launching a jet of flame far across the screen. You can duck under the first and third flame thrower's shots, but the second flame thrower crouches low to the ground when he fires. Ultimately, it is better to leap over the flames then to duck under any of them. Not only won't you have to worry if the flame thrower decided to crouch, but it will bring you that much closer to them in order to attack them. All it takes is one stab to bring them down. After you defeat all three, you will be treated to the ending where you rescue the POWs, before being sent back to the first stage again at a higher level of difficulty.
This stage appears to take place at dusk on the NES version. The same strategy about using the upper levels of the warehouses apply, although you can just as easily stick to the middle level and be fine. Be sure to take out the yellow gun soldiers every now and then as they are the only ones who will follow you up to those levels. There are no grenade launchers to worry about. Even as you reach the wooded area, there are no additional enemies like grenade throwers to worry about. After the first wooded area, you'll reach a section of land mines. You will have to jump and stab a combat specialist over almost every one. After the third mine, stop and let the yellow gun soldier approach you. Take him out instead of jumping over him, you never want a gunner behind you. Another gunner will appear after the mines have stopped, but the combat specialists continue to show up. Yet another gunner appears when you reach the cement wall. Those are both good times to throw a grenade. When you reach the brick wall, you will have to fight through groups of three combat specialists. You should be able to take all three out in a single jump. Alternatively, you can continuously run forward and let all of them leap over your head. When you reach the end, the boss will consist of three parachute gunners. They will fire on you as they drop down. Run to the right before they appear, and slowly make your way back to the left while the fire on you. Squat down on the left side of the screen, and allow them to approach you while you stab at them to get rid of them.