What distinguishes an un-baffled, or "smooth bore," cargo tank from other liquid tanks?

49 CFR 383.119(c); AAMVA CDL Manual Section 8.2.5, "Un-baffled Tanks," p.8-8-2

Un-baffled tanks ride very differently from baffled ones because there is nothing inside to control the liquid's momentum. Drivers who don't recognize this before pulling out can be caught off guard by a sudden surge that pushes the vehicle at a stop sign or intersection. Knowing the construction type before driving is the first step to handling it safely.