Crossbows are coming to Battlefield 3 in the next expansion, Aftermath. A new post on the Battlefield blog outlines the strengths and weaknesses of the new weapon, which has the power to both kill silently and blow holes in walls thanks to multiple bolts ammo types.
Standard bolts can kill at medium at short range, balanced bolts can kill at long range, scan bolts highlight enemies within a 10 meter radius of the impact site and explosive bolts create a small C4 explosion at the point of contact. You can switch between ammo types "on the fly."
DICE say that the crossbow is designed to be flexible rather than powerful. "The four different bolts and the crossbow become a jack of all trades solution suitable for any class," say DICE While none of the available bolts are as powerful as the standard weapons they mimic (a genuine sniper rifle will always be more powerful than a sniper bolt, for example), the ability to switch bolt types on the fly means any class can adapt to any situation."
If you're a premium member, you can log into Battlelog to see a new two minute video showing all four bolts in action. There's a sequence where the crossbow is used to pepper a chopper with explosive charges, eventually bringing it down. The standard and balanced bolts are almost silent, but will suffer from relatively severe bullet drop. You'll have to reload between every shot, of course.
Aftermath will be with Premium members on December 4 and released to standard players on December 18.