This is the rhythm of the bugle call used in the British Army to signal the beginning of the meal. As with all bugle calls, it had its own conventional words which all soldiers knew. They were :
This call is actually the Second Meal Call. The First Meal Call is the famous Oh, come to the cookhouse door, boys, come to the cookhouse door, which is the signal for the orderlies to go and collect the troops’ rations from the cookhouse. So the one the soldiers wished more fervently to hear was the Second!