On 17 December 2014, President Obama and President Raul Castro announced the historic decision to put decades of Cold War hostility behind them and re-establish long-frozen diplomatic ties.
The move caught most people by surprise.
But one of the few who knew it was coming was the US Charge d'Affaires in Havana, ambassador Jeffrey DeLaurentis.
"It was just an extraordinary day, as you might imagine," says ambassador DeLaurentis.
"I spent the very early part of the morning seeing off Alan Gross," he says in reference to a prisoner swap that saw a USAID sub-contractor in a Cuban prison on espionage charges exchanged for three Cuban intelligence agents in jail in the US.
He then gathered his staff at the US Interests Section to tell them of the dÃ©tente.
"Everyone erupted into thunderous applause and at that moment I knew that we were on a whole new journey. You could just feel the sea change."
There was little time to dwell on the news or celebrate.
By January, a high-level diplomatic mission from Washington was in Havana for the first of several rounds of talks towards normalising ties.
There were some thorny issues on the table, as well as some initial practical difficulties.
"We hadn't had this sort of negotiation in over 50 years so we obviously had to develop a certain level of trust and confidence," recalls the ambassador.
The Cubans raised their key questions, including the future of the Guantanamo naval base, the US economic embargo on the island and the inclusion of Cuba on a US list of state sponsors of terror.
The State Department soon removed Cuba from that list and by July, both sides were ready to restore full diplomatic relations.
Did Washington's top diplomat to Cuba ever think that it might not happen?
"No. I don't mean to imply that the issues we had to work through were easy because they weren't," he told the BBC.
"But frankly I never doubted that we would get to the point we did in July."
Less than a month later, John Kerry became the first Secretary of State to visit Cuba since 1945 and reopened the embassy.
Ambassador DeLaurentis picks out the presence of the three marines who had lowered the flag in 1961 as a particular highlight.
He also recalls the mixture of Americans, Cubans and Cuban-Americans in the audience as he stood at the podium.
"At that point I realised that what we were really talking about here was reconciliation - that's pretty dramatic in my business," he adds with a wry smile.
Since the thaw was announced, there has been a subsequent rise in immigration to the US, often via Ecuador, and from there overland to the US border with Mexico.
Many Cubans hoping to flee to the US are fearful that special immigration privileges they receive as Cubans - under the "wet foot, dry foot" policy and the Cuban Adjustment Act - will soon disappear now that the two nations are becoming friends.
I put it to the ambassador that many would-be migrants now see this as a race against time.
"We have no plans to change our migration policy and that's the message the Cuban people need to hear and absorb," he told me.
That may be Washington's message, but many Cubans simply aren't hearing it.
Around 4,500 Cuban migrants are stranded in Costa Rica amid a stand-off with Nicaragua over their route north.
Meanwhile Ecuador has reinstated a rule requiring all Cubans to obtain a visa to visit and doctors have been told they need special permission to leave the island.
An apparent crackdown on outward migration in the wake of the thaw has begun.
That this year has been significant at a diplomatic level is in little doubt.
But the key obstacle to "normal" bilateral relations, the lifting of the US economic embargo on Cuba, still hasn't happened.
The US Congress is the only body which can take that decision.
President Obama has urged them to do so but some members of Congress want Cuba to take steps over human rights first.
As a result, there are no more products on the supermarket shelves in Cuba than there were before last December's announcement and most people say their monthly incomes haven't improved either.
2011: 2.1% (Latin American average: 4.7%)
2012: 2.1% (2.9%)
2013: 2.1% (2.7%)
2014: 2.1% (0.9%)
2015 Forecast: 2.1% (0.4%)
2016 Forecast: 2.1% (2.0%)
Source: World Bank
Little wonder many ordinary Cubans say the new diplomatic relationship has made little difference to their lives so far.
"What I've heard is a lot of hope. Maybe some of it was initially unrealistic in terms of the pace," admits the ambassador.
"But I think overall people are hopeful. Even after all these years there remains a reservoir of goodwill towards the United States."
Asked if he thought the embargo's days were numbered, though, he took a typically diplomatic position: "It's very hard to say."
Within the year, there will be another president in the White House.
Republican presidential candidates Marco Rubio and Donald Trump, among others, have opposed the move to re-establish diplomatic ties.
The US broke off diplomatic relations with Cuba in 1961 after Fidel Castro and his brother Raul led a revolution toppling US-backed President Fulgencio Batista. The Castros established a revolutionary socialist state with close ties to the Soviet Union.
The following year, the US imposed a trade embargo covering nearly all exports to Cuba. This was expanded by President Kennedy into a full economic embargo that included stringent travel restrictions.
The embargo is estimated to have cost the Cuban economy more than $1.1tn and the US economy $1.2bn a year.
In September, the US announced eased restrictions on business and travel with Cuba, the latest move by President Barack Obama to improve relations with the country.
US businesses will now be allowed to open up locations in Cuba.
But the ambassador wouldn't be drawn on the race for the presidency.
"It's my hope that when whoever is elected president enters the White House, he or she will make the determination that this was the right course because it's in the best interests of the United States," he says.
Maybe so, but others fear that the hard work put in to rebuild mutual trust could be easily undone.
A visit by President Obama to Cuba before he leaves office would certainly help cement the new relationship.
Again the Charge d'Affaires in Havana was reluctant to comment too far: "Any president who's taken this historic step to change dramatically a bilateral relationship I imagine would contemplate (a visit)."
If so, 2016 could be even bigger in Cuba than last year.
The past year has been perhaps the most significant in Cuba since the fall of the Berlin Wall.