The phrase "marching the cannon mouth" may seem confusing to spell, but with the help of IPA phonetic transcription, it becomes clearer. The first word, "marching," is phonetically transcribed as /ˈmɑːrʃɪŋ/. The second section, "the cannon," is easier, being transcribed as /ðə ˈkænən/. Finally, the last word, "mouth," is transcribed as /maʊθ/. So, putting it all together, we get /ˈmɑːrʃɪŋ ðə ˈkænən maʊθ/ - a phrase meaning to move a cannon on foot.