"duty man" meaning in English

{
  "forms": [
    {
      "form": "duty men",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "duty men"
      },
      "expansion": "duty man (plural duty men)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "dutyman"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2012, Allan Grice, Call the Fire Brigade!: Fighting London's Fires in the '70s",
          "text": "Sub Officer Jack Hobbes had checked that everyone who was meant to be there was present, and detailed who was riding the Pump and the Pump Escape, who were the drivers, who were down as BA wearers and who was duty man for the shift.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative form of dutyman"
      ],
      "id": "en-duty_man-en-noun-o4VY~EOk",
      "links": [
        [
          "dutyman",
          "dutyman#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "duty man"
}

{
  "forms": [
    {
      "form": "duty men",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "duty men"
      },
      "expansion": "duty man (plural duty men)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "dutyman"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations"
      ],
      "examples": [
        {
          "ref": "2012, Allan Grice, Call the Fire Brigade!: Fighting London's Fires in the '70s",
          "text": "Sub Officer Jack Hobbes had checked that everyone who was meant to be there was present, and detailed who was riding the Pump and the Pump Escape, who were the drivers, who were down as BA wearers and who was duty man for the shift.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative form of dutyman"
      ],
      "links": [
        [
          "dutyman",
          "dutyman#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "duty man"
}