Survive The Train Tunnel Mission - How?

[Survive The Train Tunnel Mission - How?]

There are "trenches" in the rails you can stand in when the train comes. One also contains a switch to turn off the force fields.

I got that you could hide in the tunnels, but can't go anywhere because of the forcefield. Where is the switch at in the tunnel? Because like I said I looked around (Including in the tunnels) for the better part of an hour.

[Survive The Train Tunnel Mission - How?]

I decided since this was my first time playing Carrier Command to do the campaign before jumping into the Strategy game part, however after getting a couple missions in to the Train Tunnel, I was unable to continue. I explored the tunnel for about 30 minutes before reloading a previous save and trying again, but still cannot figure out what I'm supposed to do.

Is something not working or is there something else I need to do? The game is great but it has absolutely no explaination of how to play it.