'Have you news of my boy Jack? '
Not this tide.
'When d'you think that he'll come back? '
...
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Kipling wrote this after his son, Jack, went missing on a war. He was the one who pursued his son to join the war despite Jack's vision difficulties. Jack never came back.
The mother asks questions about her son Jack, who is serving in a war (probably the First World War) , but she gets no definite answer, just 'Not this tide'. She asks if anyone else has heard news of Jack-'Not this tide'. Kipling's son, Jack must have been a brave man, who 'did not shame his kind'. His parents can be proud of Jack. The question-and-answer structure of the poem reminds me somewhat of 'Uphill', by Christina Rossetti.