Sherman turret question

[Jason Ginn]

Hi,

In the "Pictorial History of the 8th Canadian Hussars (Princess Louise's)" 1973, there is an image on p.147 of a knocked out Sherman that was taken in the Liri Valley, May 1944.

I was wondering if anyone can identify the rectangular bulge on the right side of the turret. It doesn't look like stowed kit or a door, but i may be wrong.

I am completely stumped and have had no luck searching either the 'net or the few Sherman books that I own. I did however notice a clip on one of the History Channel shows today that showed another Sherman with this feature.

Thanks,

J