You want to boost this one on the second mission. During this mission you will be able to pick up several grenades. Do so, it'll make destroying the tower so much easier.
From the start:
Go to the left. Kill the soldiers behind the sandbags.
Go up and to the right.
On the far right there are another few soldiers behind sandbags. Kill them as well.
Go up: you get to a point where there's the tower in front of you and a minefield to the right of you.
Just throw a few of the grenades the game provides at it. It will take 2 or 3 grenades to destroy the tower. Immediately reset and repeat.
Will take about 20 minutes (including load times).