On this page of our guide to Sniper Elite 4 you will find out how to damage the fifth tank and how to destroy the third and fourth rockets as part of the final mission of the game - Allagra Fortress. These are the last steps, after which you will be able to complete the main campaign in 100%.
Return to the eastern hall. On the upper level, in the north-western corner of the hall, there is a corridor and an exit (M8,12). Watch out, because at the end, there is a sniper (M8,13). Eliminate him after he leans out and dash by him.
It pays off to damage the orange unit, which will compensate for the noise of your gun. This may also attract several opponents. Hide behind the low wall of the stairs, kill them silently one by one and hide the bodies behind the wall, or set trap on the stairs. Watch out, though, because on the bridge below (North) there is another sniper. You can eliminate him with the pistol.
While here, destroy also the three rockets (M8,11) on the yard, by shooting at them. Finally, use the switch on the pillar (M8,15), to blow up the central tank. Now, go to the upper floor of the glass room in the bunker, where you will radio your HQ (M8,16).
Note - before using the radio, it is a good idea to reload your weapons, heal and switch to standard ammo.
And now, for the last stage of the mission - destroying the enemy plane. You can do that while it is on the taxi way, or later on, after it takes off. If you shoot it down using the automatic rifle, you can unlock the secret trophy The Path of Most Resistance. All you need is two accurate shots from Springfield into the engines to crash the plane.