Hopkins may be right about "bombing," which in WWI could even refer to the tossing of grenades. However, the version I learned long ago goes,

             Bombed last night! Bombed the night before!
             We're gonna get bombed tonight
             If we never get bombed any more!
             When we're bombed, we're scared as we can be!
             Oh, God damn the bombing planes from Ger-man-ee!   

             They're over us! They're over us!
             One shellhole for the four of us!
             Glory be to God that three of us can run,
             So one of can use it all alone!