Niels Peter Henry Nielsen was born at Rockhampton, Queensland, on 26 November 1886. He worked as a railway porter before enlisting for a five-year engagement with the Australian Naval Forces in 1908, where he served as a stoker. In 1913 Nielsen rejoined the ANF, now the Royal Australian Navy (RAN). After completing his nine-month engagement he again enlisted shortly after the outbreak of the First World War. In what was originally to be a six-month engagement, Nielsen served with the RAN for the next five years.
Nielsen was made a stoker on the light cruiser HMAS Sydney and was serving on the ship when she encountered the elusive German raider SMS Emden on 9 November 1914. The battle that ensued between the two ships later resulted in the fledgling RAN's first naval victory. When the Sydney reached port at Colombo Nielsen took time to send a letter home to his parents with details of the engagement, including the damage that the superior firepower of the Sydney had caused to its opponent.
Nielsen spent the next three years serving on the Sydney and was discharged in 1919. Several years later he wrote a more detailed account of the battle with the Emden. Niels Nielsen returned to Rockhampton after the war and later died there in 1965.