WW1 Munitions -- Ever hear of a JJ Can?? JJ Con??

[boomer656]

Apologies in advance if this is the wrong forum for this question.

I'm reading a document written by a soldier in the AEF (141st Infantry, 36th Division) regarding action near St Etienne, FR on 11 October 1918. In this document he twice mentions what appears to be "JJ Cons" or "JJ Cans" hitting all around them. I'm thinking this is some sort of mortar or artillery fire but that's way out of my area of expertise. I'm hoping somebody here can tell me what it is he was reporting on.

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