
Right, 'expert' comments here we come!!!
There were 2 T14's, one was the precursor to the M2. It was the prototype/test-bed vehicle that led to the standardization of the halftrack. The vehicle above is not that. You can see from the photograph below, taken in December 1940, that they are different in many ways.
The other T14 never got off the paper design stage. It was for a 10 ton vehicle with armoured sides and roof.
All I can think of is that this is a (French?) post-war conversion to turn M2's into some sort of anti-aircraft system?
One thing it is not is a T14!