I've been sitting here on and off for the last couple hours, wracking my brain for Grampa episodes. I have The Simpsons on in the background (as I am wont to do), but still couldn't narrow it down until this hint. Now I think I've got it.

Abe gets a girlfriend at the retirement castle, but she's a hussy who only likes him for his access to a car (Homer's) and his ability to drive. When Homer revokes access to the car, she dumps Abe for another guy who has a car. She and the guy go on a trip and Abe steals Homer's car with Bart to follow her. Abe ends up confronting her in a surprise twist after making it seem like he was going to beg for her back.

Did I get it? I'm still not 100% sure. Until this hint, I was heavily leaning toward the Flying Hellfish episode, since "battleship" and "military" are thematically linked.