What kind of tank? An M-10?

That's an M10 3" Gun Motor Carriage (Most US military nomenclature did not use hyphens). 

Officially, it's a self propelled tank destroyer and not a "tank" per se.

It's an earlier production variant as evidenced by the so-called "duckbill" turret counterweights. 

Yes.

Not a tank in that its not armored to resist anything other than shell fragments and small arms fire,  As T26E4 said, the M10 is more like self-propelled artillery.  Same concept as a Marder I for the Germans.