My grandfather Percy Eastland.
Lied about his age, signed up in '14, sent to France in early '15. Fought in several major battles, including the Somme, where he got his first wound (bullet in the chest) when attacking and taking a machine gun position. Invalided out of the army in late '17 after his leg was blown off. Refused to talk about his experiences; only after his death did any information about his activities come to light. (He occasionally crawled out into no-mans land, usually without a weapon, to spy on the enemy positions.)
During the second world war, he worked as a mechanic in the naval dockyards during the day and a fire warden at night. During the Blitz, he dived into the harbour to rescue someone that had fallen in the water. Despite only having one leg, he was a powerful swimmer; he rescued the man and lifted him out of the harbour on his own. He didn't tell the family; they found out a couple of months later when he received another medal to go with those he received in '19.
My great uncle Ernest Mitchell.
He was a PO in the navy; and assigned to a new submarine, HMS Thetis. Unfortunately, there was a manufacturing flaw on the torpedo tubes, which they didn't know about. He had been designated to a different position during the maiden voyage, so his experience was not available to prevent a tragedy. However, he realised what had gone wrong, made his way to the flooding compartment and somehow managed to lock the water tight door to save the lives of everyone on board. Sadly to no avail; they were stuck on the bottom of the sea and succumbed to carbon dioxide poisoning.
As an aside, 70 years later, I was talking to a member of my then IT team. It turned out that he had a great uncle that served on board the same boat after it had been put back in service as HMS Thunderbolt; and had gone down with her in action in the Med during '43.