An underslung rail allows weapon accessories to be attached to the underside of a firearm. Many accessories such as foregrips, bipods and flashlights are compatible with rails.

The rail was implicitly used in Battlefield 2, Battlefield 2142, and Battlefield: Bad Company 2 for their respective assault rifle attachments.

Battlefield 3Edit

Underslung Rail
"Used to attach underslung grenade launchers and shotguns. Without it, these weapons will be equipped stand-alone."
Attachment slot	Primary
Available on	Assault Rifles
Unlocked at	Default (Assault Rifles)
Special feature(s)	Allows slightly faster access to the M320/GP-30 and M26 MASS

Available for most assault rifles, the Underslung Rail allows either the M320/GP-30 or M26 MASS to be mounted to the rifle instead of being used standalone, decreasing the time needed to switch between the two weapons. Any optics mounted to the rifle can also be used with the underslung weapon, though the M26 benefits more from this property. The rail is not available on any of the bullpup style firearms except the AUG A3.

While using the underslung weapon, the soldier carries the weapon in a manner suggesting its use. M320/GP-30 users will tilt their weapon back, while M26 MASS users will flip out the weapon's left-hand bolt.

If a Medkit is selected, the rail will have no effect whatsoever. Also, certain combinations of weapons cannot be mounted together:

• M26 MASS with AN-94
• M26 MASS with AEK-971
• M320 with G3A3