Prince Harry has been deployed to Afghanistan for four months, the Ministry of Defence says.
The prince, an Apache helicopter pilot, arrived on Thursday night at the main British base, Camp Bastion in Helmand.
The 27-year-old, who is third in line to the throne, will take part in combat missions against the Taliban.
It is his second Afghanistan deployment - he spent 10 weeks in Helmand province in 2007-08 but was pulled out after media reported his secret deployment.
Captain Wales, as he is known in the military, arrived as part of the 100-strong 662 Squadron, 3 Regiment, Army Air Corps.
Royal Navy Captain Jock Gordon, Commander of the Joint Aviation Group, said: "Captain Wales, with his previous experience as a Forward Air Controller on operations, will be a useful asset.
"He will be in a difficult and demanding job. And I ask that he be left to get on with his duties and allowed to focus on delivering support to the coalition troops on the ground."
Prince Harry is the first member of the Royal Family to see active combat since his uncle Prince Andrew fought in the Falklands war.
The prince, who turns 28 next week, qualified as an Apache helicopter pilot in February this year after 18 months of rigorous training in the UK and the US.
The Ministry of Defence regard the threat to Apache aircraft and crew in Afghanistan as "low".
The Taliban claim to have brought down an Apache in Afghanistan, but the British have never lost an Apache anywhere, from a total of 67, despite two minor crashes.
The Apache attack helicopter is designed to hunt and destroy tanks and is equipped with rockets, missiles and an automatic cannon.
During his previous deployment, Harry was a forward air controller, directing planes dropping bombs on Taliban positions in Helmand province.
The Ministry of Defence, which had agreed a news blackout with British media believed that the risk to the prince was too great after Australian and US media revealed details of his deployment.
Then he was part of ground forces, calling in air strikes against enemy positions. He was disappointed to be withdrawn, and determined to return to front-line combat.
In April, the prince suggested it would be pointless to train as a helicopter pilot if he never served.
"I'd just be taking up a spare place for somebody else if they didn't have me going out on the job, " he said at the time.
The Society of Editors, which arranged media coverage of this latest deployment, said news organisations had behaved responsibly.
The society's executive director, Bob Satchwell, said: "The details were not reported even when the row broke about the Las Vegas naked Prince pictures.
"It would have been so easy to say he was partying before flying out to war, but the secret was kept until the time agreed."
The BBC's Royal Correspondent, Nicholas Witchell, believes the announcement may alter people's opinions about the Las Vegas pictures.
"Perhaps that explains why he was just a little bit too carefree on that occasion, his final foreign outing before he knew that he was off to Afghanistan," he said.
Camp Bastion is a sprawling base in Helmand and one of the largest in Afghanistan, reports Quentin Sommerville.
Harry's living quarters will be a shipping container, shared with another member of his squadron. Although basic, it is far better accommodation than the tented barracks that others, who are not Apache crew, have to sleep in.
Bastion has a bar which does not serve alcohol as it is forbidden on base. It has table football, a pool table, and games. Elsewhere on Bastion there is a cigar bar and a steak restaurant, called Blues.
Those working on the base are regularly awakened by the distant sound of heavy ordnance being disposed of, and a 5am call to prayer from a loudspeaker on top of the local mosque.
Recently Harry has had a high-profile presence at the London 2012 Olympic Games. He then went to Las Vegas on a private holiday, where he was photographed naked at a party.
The photos, published by the Sun newspaper and international websites, prompted about 3,800 complaints to the Press Complaints Commission.
However, the watchdog said it would be "inappropriate" to open an inquiry because the prince's representatives had not yet made a formal complaint.