I would advise attempting this on the first play, which allows you to get all the progression achievements, this one and complete Hard mode in 2 plays.
Not really that hard; if you are finding it difficult to run through an area with many enemies try hiding round corners and letting them come to you one at a time.
The last sequence (in the server room) is very difficult without using guns, just take your time and take each enemy out individually.
There is a soldier with a .50 cal (well, some sort of heavy machine gun) directly between you and the door who will not move, run at him from either of the two side walkways (as opposed to the forward facing one) and try and counter him first time. May take several attempts, depending on how good your timing is. Mine's not great so I had to replay it maybe 20 times.