Forty veterans of the World War II Arctic convoys have become the first recipients of a new medal.
Prime Minister David Cameron hailed the men as a "group of heroes", as he presented them with the newly-created Arctic Star.
The Arctic convoys, reportedly called the "worst journey in the world" by Winston Churchill, took supplies to the Soviet Union from 1941 to 1945.
More than 3,000 men died while on the convoys.
Cdr Eddie Grenfell, 93, was given his Arctic Star at a special ceremony in Portsmouth earlier as he was too ill to travel to the ceremony at Number 10 Downing Street.
Convoy veterans were previously eligible for the Atlantic Star but Cdr Grenfell campaigned for 16 years for a specific Arctic medal. Its creation was announced by David Cameron in December.
The 93-year-old said it felt wonderful to receive the medal and that it would be "churlish to ignore" the part played by Mr Cameron in its creation.
Presenting the medals, the prime minister said: "I can't think of a prouder day that I have had in this job or a group of people I am more honoured to share it with.
"I am only sorry that it has taken 70 years to get to here and to say thank you."
Frank Bond, 89, from Eltham in south east London, said: "It's the culmination of 72 years since I first went on the Russian convoy, to recognise not what I did but what the sailors who gave their lives did.
"I am not a hero, I am a survivor but the guys who went up there, they really had it rough and a lot of them didn't come back."
The prime minister also joined three Arctic convoy veterans for a tour of HMS Belfast, which celebrated the 75th anniversary of its launch last weekend, as they showed him where ice was cleared from the deck in perilous circumstances.
Members of Bomber Command were also awarded the newly-created Bomber Command clasp at a separate Downing Street ceremony.
Mr Cameron also described how 55,000 of the 125,000 people who joined Bomber Command lost their lives.
He said the decision to create a Bomber Command clasp was the right one, telling veterans and their families it had been vital in defeating Nazi Germany.
Among the Bomber Command veterans was Doug Radcliffe, 89, from Hampstead, north west London.
He said: "We are deeply honoured. It really is an honour to be here, a very special day.
"It's not just a clasp, it's an honour.
"It adds to one of the things that's been missing for 60 or 70 years."
The decision to award the clasp followed recommendations of a review of military decorations by former diplomat Sir John Holmes, who also concluded that Bomber Command had been treated "inconsistently" with their Fighter Command counterparts.
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