P-38 .50 Gun Barrels/Blast Tubes

I have a question regarding the .50 cal gun barrels on the P-38. In later versions of the P-38, the gun barrels appear to be fitted with silver colored, solid blast tubes (similar to those on the P-47). In earlier versions of the P-38, the barrels where exposed (circular cooling holes in the barrel jackets).



Does anyone know why the blast tubes or sleeves were fitted to the .50 cal barrels? I have looked for an explanation in the publications I have on the P-38, but can't find anything that refers to it.

I have posted this question on a number of Forums and thought I would post it here as well.



Thanks.



Ron

They were put on to improve the aerodynamics of the a/c, or clean them up so to say.

Soren,

Thanks for your reply. The use of the blast tubes to increase aerodynamics makes sense - although this is the first time I have heard that this was the reason for using them. Where did you come across this information?

Thanks.

Ron

In addition, I think the P-38M night fighters had some sort of blast tube to hide muzzle flash.