Warhammer 40K Tabletop VII: Common Sense is not RAW.

[Arcanoi]

Page 51. Combat Squads is an ability that a whole smattering of Space Marine squads have. It lets you split your 1x10 squad into 2x5 squads, while still having the advantages of 1x10, namely the ability to take a Heavy Weapon and take up only one Force Org slot.

So you take a Rhino/Razorback, and you can put one 5-man squad into it, with a Sergeant and a Flamer or similar special weapon, and the other squad can hang back in cover with a Plasma Cannon or Missile Launcher.