Campbells first marketed their Cream of Mushroom soup in 1934, but snapbean casserole recipes go back before then. I have one that calls for cream sauce, but says cream of mushroom soup may be used as a substitute.

Green Bean Casserole

2 pkg. French-style frozen beans, thawed
1 can water chestnuts
1 can bean sprouts, drained
1 large can sliced mushrooms
1 med. onion, chopped.
2 cups medium cream sauce
   (or cream of mushroom soup)
Salt to taste
Grated cheese to taste.
1 can French-fried onions.

Layer half the beans, water chestnuts, bean sprouts, mushrooms and onions in 2-qt casserole. Cover with half the cream sauce; sprinkle with salt and cheese. Repeat layers. Bake at 400F for c. 20 minutes. Top with onions; bake for 10 minutes longer or until bubbly. Sherry may be added. May be prepared a day ahead and refrigerated.

From Beta Sigma Phi Holiday Cookbook. (no date)

Campbell's Classic Green Bean Casserole

1 can (10 3/4 oz) Campbell's Condensed Cream of Mushroom soup
(regular, 98% fat-free or Healthy request)
1/2 cup milk
1 teaspoon soy sauce
Dash ground black pepper
4 cups cooked cut green beans or 2 pkg frozen, thawed
1 1/3 cups French's French Fried Onions

Stir soup, milk, soy, pepper, beans and 2/3 cup onions in a 1 1/2 quart casserole.
Bake at 350F for 25 minutes or until the bean mixture is hot and bubbling. Stir. Sprinkle with the remaining onions.
Bake for 5 minutes or until the onions are golden brown.

www.campbellskitchen.com/recipedetail.aspx?recipeId=24099

Reminds me of the broccoli-French Fried Onion-Cream of mushroom soup casserole recipe we occasionally use, from the classic White Trash Cooking.