'Scratch my back'

My grandfather was a Sherman tank commander on Iwo Jima, and he told me about the tankers' term 'scratch my back.' Japanese infantry would climb all over the tanks, trying to pry open hatches and drop in grenades, pour fuel down the ventilators, damage the engine, etc. When that happened, the tank commander would radio a nearby tank and ask him to 'scratch my back,' which meant he wanted the other tank to shoot the Japanese infantry off of his vehicle with small-caliber weapons.

I have watched a lot of WWII documentaries and read many books on the subject, especially WWII tanks, and I never could find any mention of 'scratch my back' in any of them, until I saw the episode 'Man and Machine.' According to the soldier they quote on the show, the tanks would spray each other down with machine-gun fire; my grandfather told me that the tanks were also issued with short 12-guage shotguns that they would use in close quarters to clear enemy infantry off the other tanks.

I'm just surprised that I never saw the phrase mentioned anywhere else, until this particular show. Have any other military/tank enthusiasts heard of it anywhere but this show?

- You may have come on no bicycle, but that does not say that you know everything.