When Harry joined the Navy he left his home close to the River Thames, just a few minutes walk from the Royal Naval College in Greenwich. His mother had been widowed for many years and his older brother, Dick (in the Army) would eventually be killed in action in Italy. His sister Doris joined the WAAF and his other sister, Emily (whose husband would also be killed in the war), remained in Greenwich. The youngest brother George was also in the navy.
Harry had always wanted to join the Royal Navy and had badgered his mother for a long time to let him go and to make the Navy his career. When , finally, his mother agreed, war was very close. He was accepted and sent to HMS St. George on the Isle of Man for twelve months training in the boys service. Once he had completed his training he was drafted to his first ship, HMS Dunedin.
This report appeared in a Greenwich newspaper after Dunedin had gone down:
“LOST HIS LIFE AT SEA. Aged 17, Henry George Brennan, first-class boy on HMS Dunedin was reported missing last November, and now his parents living at 37, Woodlands Park Road, Greenwich, have been notified that he is presumed to have lost his life in action. An old boy of Randall Place School, Greenwich, he joined the Navy at the age of 16, and had been nine months at sea when he lost his life. He has a brother who has just gone overseas with the Forces”.