Bolt Action ZSU M-17 AA Halftrack

K,

here's the one you're thinking of, the T28E1:

link

link

I remember reading somewhere years ago that the gunners of the T28E1s in North Africa quickly figured out that Stuka pilots would hold off from committing to an attack if they thought the ground troops they were targeting were armed with anything heavier than a .50 cal. machine gun. As the .50 cal. fired a tracer round, the T28E1 gunners would refrain from firing their 37mm cannons, using only their twin .50s. The Stuka pilots the story goes would see only .50 cal. tracers, think that they had a safe margin to dive in closer to the attack for greater accuracy, and commit to their dives, at which point the T28E1 gunners would let fly with the 37mm cannon, much to the discomfiture of the Stuka pilots who had been snookered into the range of the American automatic cannons.

Probably apocryphal, but I suspect that the fact that the M16/17 configuration came to replace the T29E1 configuration, so the arrangement must not have been as effective as its designers had hoped.

Hope this helps!

Leland R. Erickson
Metal Express
metal-express.net