Or maybe Voltron…

If our PCs happen to be part of a vehicle squad….

On page 258, we see the nearest orks drop off their towers and charge. The other orks drop off their towers and….

Transform into a battlewagon!!

"VEHICLE SQUADRONS
Replace the second wave of Orks with a Battle Wagon (see page 244). It still takes 3 combat rounds to reach the combat. "

The other alternative is that the battle wagon was standing guard in the other watchtowers and not orks…

Perhaps this should read:

"Add a Battle Wagon (see page 244) to the second wave of Orks. It still takes 3 combat rounds to reach the combat. "

or

"Mount the second wave of Orks on a Battle Wagon (see page 244). It still takes 3 combat rounds to reach the combat. "

or

"Replace the second wave of Orks with a Battle Wagon (see page 244). It still takes 3 combat rounds to reach the combat. The remaining Orks charge out 3 combat rounds after the battle wagon arrives. " (this conflicts with the Nob and Grots though who would then come out earlier than the Orks)

I can't imagine the remaining orks diving down off their towers in a frenzy to get into combat, and then deciding suddenly to sit back and play a game of cards while the battlewagon goes ahead instead.

Incidentally, while a battle wagon is a fair competitor for a Leeman Russ, it's a bit rough for the other vehicles such as a Sentinel or Hellhound team. You may want another option for them.

I had an issue with that wording too.

It seems to me that the best options are:

"Add a Battle Wagon (see page 244) to the second wave of Orks. It still takes 3 combat rounds to reach the combat."

or

"Mount the second wave of Orks on a Battle Wagon (see page 244). It still takes 3 combat rounds to reach the combat."

As for Vehicle Squads that have something lighter than a Russ, a few Warbuggies or Warbikes seems sufficient.

When Running the adventure I took the "easier" way of just replacing the 21 orks with the battle wagon.

It scared the Hell out of their Flame tank but they used it as bait to let the weapon specialist close in with his melta gun.

This raised the question of Open topped vehicles, is the whole Battle Wagon open toped or just the transport part???

By RAW, a Battle Wagon needn't be armed with anything particularly spectacular, which goes a long way to explaining why the designers thought such vehicles would be balanced against Hellhound or Sentinal squads, as the GM is under no obligation to arm them with a Kannon or Lobba and can instead rule that the PCs have stumbled upon the Orks' most powerful heavy machine gun carrier, with a pintle Big Shoota and two sponson Big Shootas, for example…

Still, just for variety's sake it seems like it'd be a good idea to make the Battle Wagon that replaces the second wave of Orks at the refinery instead be a Trukk for players in light vehicle squads. Obviously though, a second Wagon is still going to be neccessary if the players are driving a Russ…