Snake's Revenge/Part 3

Enemy camp
You will now find yourself in the enemy camp. Your rank should have risen to 3. There are many mines on the ground in this area, so you would do well to keep your mine detector equipped at all times to avoid them. Go north for two screens. You will receive a call on the transceiver, but if you try to answer it, you will find that the battery is dead. You will therefore have to find another one. There is also a door on this screen, which you cannot open with any Pass Card, so ignore it. Go north again and open the door on the right with Pass Card 3. Inside you can stock up on grenades and you'll find a new battery. Then return to the previous screen to answer the call. The pilot will tell you that there is a secret entrance somewhere in the ground. Then go north for two screens. Open the door on the left with Pass Card 1 to stock up on rations and guided missiles. By opening the door to the north with the same Pass Card you can free a prisoner, who will tell you to beware of John. Then go right and open the door to the north with Pass Card 2 to fill up on oxygen tanks. Finally go south and open the door on the right with Pass Card 2 to stock up on plastic explosives.

At this point, you have explored the whole area and you must find the secret entrance. You will find that the yellow sandbags on the various screens can be destroyed with plastic explosives or with a missile. If you destroy them, an enemy will appear in a hole and attack you with a rocket launcher. Kill him quickly, preferably using a powerful weapon, such as guided missiles or grenades. The only essential to destroy, however, is located in the screen to the north, where there is the door that leads into the room with the oxygen tanks. You will have to destroy the sandbags further to the right. Quickly kill the enemy with the rocket launcher and a hole will appear when he dies. Enter inside to continue.

Side scrolling area 2
Once inside, you will have the option to go left or right. If you go left, you will return to the enemy camp, through the door that you could not open before: do it if you have forgotten to take something. Go right to continue. You will now have to go through a long flooded tunnel, better if you have a good supply of oxygen tanks. Along the way you will have to break down two barriers. Select the gun as a weapon and press B when you are against the barrier, to place the plastic explosive. Get away before it explodes and move on. You will then have to overcome a pool of water, avoiding being seen by the surveillance cameras (when necessary, immerse yourself in the water) and jumping over the mines on the bottom. In the next stretch of water you will find another pitfall. There is a metal sensor that moves on the surface of the water. Avoid these sensors absolutely by diving. In fact, if you touch them, the alarm will sound and bombs will start falling from the ceiling. In addition, those sensors will electrify the water, making you lose some vital energy at every moment. Once you have passed the stretches of water, you will have to eliminate a single enemy, then you will have reached the end of this area.