What is that on the upper rear hull of this M3A1?

[dharper]

As I was going through the 20 or so new scans of M3A1 Satans that I located at the National Archives (II), I noticed a photo with these two Satans moving away from the camera. Please excuse the rather poor quality of the image, but this area of the picture was about 1 inch wide and I have enlarged it in Photoshop to try to get a better look at what the two strange looking devices are on the upper rear hull.

Anyone have any suggestions?

http://www.harpercastings.com/images/image_posts/83041%20cp.jpg