It's still at Bovington, in store.
The hatch is the pistol port, that's the official name but it's unlikely it was used for that purpose much. It does give another view on the world for the loader and somewhere to throw out the empty cartridges.
It was deleted from production in early 1943 but reintroduced later due to complaints from users. All Sherman models built from mid 1943 to early 1944 did not have it, Grizzlies being a prime example.