The biggest problem with the Ostie is not how tough it is, in fact if you strafe the turrent, even with .50's you will usually kill the gunner and disable the turret.
The problem is getting into a position in which you can effectively strafe it, without it shooting you down.
Its 37mm cannon is going to be a more stable, or effective, gunplatform than anything in the air, and I don't know of any single aircraft in the war that can take 37mm hits and survive.
Maybe heavy bombers, but they're even bigger targets, which means they will get hit sooner, and more times.
The only way I have found to effectively take out Osties is to pick them off from altitude with bombers , ala smart bombs style.
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Vermillion
**MOL**, Men of Leisure