Pogo wrote:
Can someone say how many crew for TBD? They seem to refer to 'assistant pilot' (?) and bombadier, and it's almost as if a third guy was in the belly or something, given what appears to be a sighting window in the belly? with it's own miniature bomb doors? (did I see correctly??).
It depends on the mission and (as JFS61 described) what point in the war we're talking about.
Despite the "torpedo plane" designation, Devastators could also serve as high(er) altitude level bombers. This tactic was used with some success against stationary targets early on .. most notably by the Japanese (it was a B5N "Kate" which dropped the 500kg armor piercing bomb that doomed the
Arizona).
In the TBD-1, the middle of three crew positions was for the assistant pilot/bombardier. There was a set of basic flight controls, but perhaps the most unusual feature was a kind of tunnel running underneath the seat and forward below the pilot. On a level bomb run, the bombardier would drop down and lay flat with nothing standing between his favorite vital organs and the enemy gunners save for a thin sheet of aluminum! A set of doors in the nose just aft of the engine would open, not to expose an internal bomb bay (the bombs were carried externally), but to allow an unobstructed view for the Norden bombsight.
Using the photos Mark kindly provided, you can start to get a sense for it ...

A wild shot looking down between the pilot's feet (note the rudder pedals) to the open bombardier position and sighting window below. The shock mounts for the Norden bombsight can be seen on the lower left center of frame.

The open bombsight doors seen from outside showing their placement between the engine and the leading edge of the wing.

Norden bombsight installed.

1000 lb bomb in place.

Two 500 lb bombs loaded.
About 14 years ago, I was fortunate to interview two of the three men who crewed BuNo 0298 (5-T-7) when it ditched at Jaluit on 1 February, 1942. Radioman/gunner RM1c James "Ace" Dalzell described how bomardier ACMM Charles Fosha detached the Norden bombsight which they then threw over the side while still in flight, deep-sixing it in the ocean where the Japanese could never recover it. Later, as a POW, Fosha was interrogated for what he knew about the still top-secret instrument, but he brazenly (and successfully) bluffed it out, saying "I'm just an enlisted man, they don't tell me about that stuff!"
Pogo wrote:
Also couldn't quite catch where the forward firing machine gun sticks out.
The single fixed forward firing .30 caliber machine gun was mounted on the right side, about midway down the fuselage.
Again, the photos Mark posted give us just what we need to illustrate the point.

With access panels removed we can see the gun as mounted (with the barrel and cooling jacket just above the carburetor air intake .. and the receiver off to the left).

Look at the ring cowl to the left (almost even with the hub) and you'll see the round opening where the fixed forward gun fires through the propeller arc.