1) What do you all use as the narrative movement rate of a Chimera? By stats it moves 70 kph, the rulebook says 10 hours is the standard march time, so 700 kph? That seems really fast, but I assume that is with clear road travel. Any ideas on a more realistic speed, say moving through medium density forest?

2) Are there any notes on how far a Chimera can go on a full tank of fuel?

3) The rulebook does not state there is any bonus for attack a vehicle in close combat. I find this unrealistic, as infantry scrambling across a vehicle allow them to exploit weak spots like exhaust ports, fuel lines, viewports to the inside. Unless I'm mistaken, 40K states that close combat attacks hit the back armor regardless of facing, this seems fair but is there something I'm missing in the OW rulebook? I think I'd also allow close combat attacks using any weapon, not just melee.

Erm...

1) If it moves 70 kph it will move 700 km after 10 hours... with a speed of 70 kph... not 700. The speed in a forerst depends on several factors. How thick is the flora, does it consist of dense trees that cant be simply drove over, has the path been cleared by pioneers are there any obstacles like swamps etc. Actually the Chimera is rather slow but sturdy. With a dozer blade it should have have that much of a problem. Even less if a tank is ahead to clear the path so take a leman russ movements and reduce it by some kph. If they are on their own I'd say around 40 kph.

2) As long as you as a GM need it. You can construct your campaign and if you want them to go dry say they have to take a very long route, if not make it a shorter route. There is no value of knowing how much fuel they carry if you can adjust the path they travel however you want it to be, Though keep in mind that a chimera will always leave its base for a mission with enough fuel to reach the target and go home with some spare fuel in addition. Also your operators should have an Idea what their chimera burns so if the guys of the munitorium issued to less fuel he should notice it. At last thats its for the normal situation.

3) The tabletop has that rule for you mostly attack with a swarm and need to apply one modifier for all dices of said swarm. In ow on the other side you controll one guy, not a swarm of up to 20 or more compatants. Standing in front of a Leman Russ, declaring that you want to hit its rear armor while you chunk your bayonett on its front would be stupid. If you want to swarm it, you have to actually swarm it, meaning that one of your friends has to go on its back. Also the rulebook can not state all rules you might need and it is up to you as a GM to fill the gaps. If you think it is okay that after your weapon specialist climbed the tank with a climbing test if necessary that the hatch would have less AP than the overall top armor, so be it. If you accept that the main cannon is damaged without the necessary result after one soldier charged the tank and managed to throw a krak grenade into the main cannons barrel, so be it.

And for the weapon choices for close combat the rulebook actually states that you have to take melee weapons or pistols. Note that you are never in melee combat with a Tank unless you want it to be. You can stand right infront of a tank without being in melee combat because he can not engage you. It would be a different thing if you stood against a dreadnought and these things are even so fast that even in the tabletop nobody can engage their back armour if in fact 20 models stand right around them. So might consider melee vehicles to always get hit in the front too.

I'm trying to stay "realistic" without too much GM hand-waving. I guess fluff wise I'm looking for the answer on the fuel issue, especially since I'm planning on sending my squads on extended behind-enemy-lines type mission in a Chimera, a task that could last weeks. At what point would they have to steal more fuel or abandon their transport?

I believe the point he is trying to make is that, as a GM it is up to you to make those decisions. When enough things have happened, either narratively or combat wise that would make sense that your team ran out of fuel, then that is when it happened.

As a GM, you really have to fill those gaps in the rules yourself and when you deem necessary (which I find as a positive much moreso than a negative).

Personally, before the mission started I would let them know exactly what they were in for. And if they CHOSE to requisition (sorry, DW talking) more fuel then I would extend in my head what would be an appropriate time frame for it to last depending on mission circumstances. If they chose to instead ask for 30 canteens of water and two nude magazines and a case of lho sticks and amasec, then they will run out of fuel MUCH faster.

And this doesn't take into account how much of their trip will be in the Chimera. If they intend to park it in a cave, and hike 30 miles to the last leg of the journey, that conserves 60 miles worth of gas, at the risk of not being able to get to the transport, if things get hairy, or if it is discovered in the hand full of days in which they might be away from it. There are so many factors that could work into it, it really is just better for the GM to arbitrate when the gas is up, whether from long driving, a defect, damage from hard travel, or what have you. Otherwise, you might just check on the Internet, and see if any websites describe how much extra fuel our own tanks frequently carry. Many things in 40K don't transplant well to or from real life, but some other things were obviously based on such real life facts and issues.

1, Speed is halved when moving through difficult terrain, so the chimera would have a narrative movement rate of 35kph when travelling through a forest.

2, IG vehicles have almost infinite range as they can run on literally anything. Like, their engines can burn piss, water, wood, corpses, not-solid mud and everything you can fit into the fuel tanks and is in a roughly liquid form.

3, You get a +30 bonus to-hit because of its size. Isn't that enough ?

I totally forgot about #2!

OP, you should make sure your players know about the resiliency of IG vehicles when it comes to fuel. Their PCs would definitely know this information. I would even make this a RP experience in and of itself. "OK, the chimera comes to a churning hault as the digital fuel display reads empty. You are in a lightly wooded area."

Then I would give extra XP to the first dude who decided to piss in the tank. :-D