An after 20mm tub for the big 1/144th scale Revell Fletcher. This will allow you to add some extra firepower to the model, converting it into a mid to late war ship. There is a blast extension on it to shield the gun crews from the blast of the after five inch mount. If your ship didn't carryt his feature, then it can be easily snipped off and lightly sanded down with a sanding stick.
The part is meant to represent that carried by USS Heerman and probably other Bethlehem-built Fletchers. Check your references to be sure that this part is right for your ship. There were many variations and versions, so checking your references is really necessary.
Note that this part has no camber. If you wish to add deck camber, a light touch with a sanding stick should do the trick. Just be careful as the part is fragile. Camber has not been added since the "tightness" of the deck and hull assembly will affect the model's geometry and thus the amount of deck camber. Another part with a small amount of camber is also available if you wish to use it instead, although again that "tightness" may or may not mean that that part will work absolutely correctly right out of the box.