Landships II

Okay, pardon me if this is a dumb question...

I was at Bovingdon last week, looking at their MkVI which had one of what I assumed were the pistol ports open. My 11 year old asked what it was, and I said it was a pistol port from which one might engage the enemy at close range with one's sidearm.

"Err" says he "how do you open it?"

So I glibly point out that the flap slid to one side, etc etc etc

"No" says he "how do you open it from the inside?"

So I looked and, yes the little cover could be moved to one side as it was hinged on the top...but there seemed to be no way to open it from inside the tank - from the outside yes, so were one the enemy one might open it and shoot inwards, but I couldn't see how it worked. So this leaves me thining that either a) it's not a pistol port (but then again what is it), b) the Bovingdon Mk VI is not standard or c) there is something really obvious I'm missing.

So I said I'd ask here to find out the answer...