P-39 37MM Cannon Jams

This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules


1st Sergeant
May 30, 2011
Cape Canaveral
I finished reading the book, Cobra Combat, by Lt Col Robert E. Case. He had something interesting to say about the P-39's 37MM gun.

The 37MM depended on gravity to extract the empty shells; it could not stand any negative G. If you pushed the nose over onto a target and fired, odds are you had some negative G. The only way to make sure that the gun would not jam was to fire it only in level flight or when pulling positive G's. So firing it in a dive meant shove the nose over, acquire the target, and then pull up a bit before firing to make sure you did not have any negative G's.

As described in the book "Druid's Circle," at the urging of the USAAF the RAF tried out the P-39's 37MM as an antitank gun in a fixed position on a firing range. Not only did the 37MM not penetrate the German tank armor, it jammed every time they fired it. They found that a part on the ejection mechanism was too long; they sawed it off and then it fired Okay.

Users who are viewing this thread