Homefront

a very easy achievement, just take your time killing the 5-6 enemies outside the church as your time doesnt start until you've walked through the church door.
once your inside and go up the stairs you will normally find two enemies downstairs below you, and 3-4 enemies across the otherside of the walkway. just remember you've got 4 minutes so no need to actually rush.
then once you've cleared the walk way you'll go up some ladders with you'll face 1-2 enemies, and once you've killed them just walk along to the crows nest and the achievement should unlock.

you should also do this achievement on easy or normal so then it will be easy.
also attached rooster teeths video guide to show you

-A Dr. Joystickler Video-
A quick guide to this easy achievement. Near the end of Ch. 5 you'll come to a church; you must make it from the front entrance to the bell tower sniper post in less than 4 minutes. It can be done on any difficulty, on easy it took a minute.