The Widowmaker (Mary May)
After the liberation of Fall's End, talk to the bartender in the Spread Eagle to launch this story mission.
Make your way to the Grain Elevator. Even if you already liberated it during the Vespiary prepper stash mission, it's in enemy hands again.
There are only half a dozen enemies here, no heavies, one VIP, and a few melee fighters. You'll want to kill them all before proceeding.
When the bipeds have been pacified (no need to kill the caged wolf), check the warehouse door, then grab the key from the little revival tent.
Hop into the Widowmaker and make tracks. This next part is one of the easiest vehicle sequences in the game, and is even easier if you have the Auto-Repair perk. Just keeping following your marker to each roadblock, and blasting on through.
The Widowmaker's guns are a little tricky to aim, but they can be useful for sweeping away minor vehicles, and for exploding fuel trucks before you ram into them. Happily, gun kills still count for your Hit & Run perk challenge.
Once you've destroyed all nine road blocks, and made a reasonable effort to avoid manslaughtering civilians, follow your marker back to Fall's End.
Park the truck in the indicated spot by the Spread Eagle, then talk to Mary May to complete the mission, and unlock the Widowmaker for use.