HMS Diamond, the third of six new Type 45 destroyers being built at a cost of £1bn each, sailed out of Portsmouth Naval Base, Hampshire, for its six-month deployment to the Middle East.
Members of the public lined the harbour walls waving flags as the ship passed by.
The ship’s mission is to carry out maritime security patrols in the Indian Ocean, Gulf of Aden and the Gulf, replacing its sister ship HMS Daring.
The ship will take part in the navy’s piracy patrols and provide reassurance to the UK’s allies in the region.
Earlier this month, Diamond entered Portsmouth Naval Base with a 21-gun salute and a diamond-shaped flypast followed by a street party on board the flight deck to celebrate the Queen’s diamond jubilee.
Defence Secretary Philip Hammond said: “The deployment of HMS Diamond this week marks another watershed for the Type 45 programme, with three of these highly capable destroyers now on operations worldwide.
“I wish her success in her Middle East deployment where the security of the international shipping lanes continues to be of the utmost importance.
“The Royal Navy continues to make a significant contribution to protecting the freedom of the seas and Britain’s interests across the globe.”
Diamond’s commanding officer, Commander Ian Clarke, said: “After completing months of rigorous training and intensive engineering trials, as well as the obvious pride in our participation in the national jubilee celebrations earlier this month, Diamond is now ready in all respects to undertake her role in her first operational deployment.
“The ship’s company has shown that this ship has the potential and capability to undertake the variety of likely scenarios we may encounter.
“Although this will be important for the ship and my people, this is not new business for the Royal Navy, which has had a continuous presence in the Gulf for many years.
“The deployment of Diamond to the region is entirely routine and replaces another ship already on patrol.”
HMS Diamond was launched in 2007 and commissioned into the fleet in 2011.
Four of the Type 45 air defence destroyers have now been commissioned and the remaining two will enter service during the next two years.