The submarine HMS Thetis was undergoing sea trials in Liverpool Bay on 1 June, 1939, after being built locally in Cammell Laird. Due to a fault in her torpedo tubes, after diving she failed to resurface leading to the loss of 99 men, including Liverpool pilot, Norman Wilcox.
The majority of those who perished succumbed to carbon dioxide poisoning whilst waiting to be rescued. Thetis was eventually salvaged four months later by the crew of the salvage vessel the Ranger, owned by the Liverpool and Glasgow Salvage Company.
The hat band was donated by the family of Alfred Roberts, who was 17 when he took part in the salvage operation. His family remember him speaking about the salvage as a harrowing experience, as he saw the dead bodies of those trapped inside the submarine.