This lethal move which will come in more than useful when you are surrounded by multiple enemies in close combat fighting is performed by pressing Y, RT. To switch back to the weapon again to do another double slash press RB and if you press RB, Y, RT repeatedly you can continue doing double slashes.
The easiest and quickest way to find items and weapons is to access the map and look for 'X's as they indicate their location. Also search near the 'X's as sometimes there will be gold pickup spots there.
If you want to increase your arsenal of weapons to include the following then complete the indicated task to get them.
Unlock M60: Visit the website findallfive.com and select the 'Join the Battlefield Community' option and sign up with Electronic Arts. When you then register for the 'Battlefield: Bad Company e-mail newsletter' you will receive a unique code by e-mail which will enable you to unlock this destructive weapon.