The American Sector, inside the National World War II Museum, could have been a theme restaurant – the hostess wears polka dots, the walls are filled with sepia-toned photos of the ‘Greatest Generation’, and the undulating metal ceiling is a nod to the Pacific Theatre – but celebrity chef John Besh flies past the trite and hits the target with food that’s both contemporary and whimsical. The menu, which includes tomato soup, sloppy Joes, and milkshakes, reads like a list of mid-century comfort food. The tomatoes, though, are heirloom, the sloppy Joe uses short ribs, and the milkshakes come in seasonal flavors like honey pear. Half the diners are visiting the museum, while the rest work at the Warehouse Arts District’s galleries, nonprofits, and start-up companies.