The Royal Navy's £3 billion aircraft carrier HMS Queen Elizabeth, dubbed 'Big Lizzie', is to set sail for the US where it will land fighter jets on its flight deck for the first time.
The landmark moment will come eight years since a fast jet last flew from a British aircraft carrier.
The 65,000-tonne carrier is expected to leave Portsmouth Naval Base at about 6pm on Saturday.
During its trip to North America, the warship will embark two US F-35B test aircraft based at Naval Air Station Patuxent River, Maryland, which are expected to carry out 500 landings and take-offs during the carrier's 11 weeks at sea.
Ahead of the crucial test run, navy chiefs pledged to protect the boat from the "eye-watering" threat of Russian submarines.
Commodore Andrew Betton, commander of the UK Carrier Strike Group, said that the carrier would be provided full protection in the face of threats from Russia.
He said: "Russian submarines are more active in the North Atlantic than they have been since the Cold War and we take that very seriously, the ship will be well protected as she makes her transit across the Atlantic.
"We will seek to operate professionally and within the standard laws of the high seas operating in international waters going about our business.
"We are not seeking confrontation, we are heading to the east coast of the United States to conduct trials."
Captain Jerry Kyd, the carrier's commanding officer, said: "The increase in Russian activity we have seen in the last couple of years is frightening and for national security reasons it just underlines why we need to maintain a balanced, strong and able, capable fleet.
"It's been quite eye-watering what we have seen in the last couple of years."
Captain Jerry Kyd, the carrier's commanding officer, said: "This deployment to the United States will be another first for my ship.
"Crossing a major ocean with 1,500 sailors, aircrew and marines embarked and the spectre of the first F-35B Lightning landing on the deck in September is very exciting for us all.
"It has been an incredible journey since we left Rosyth just over a year ago and we are all looking forward to this next seminal chapter in HMS Queen Elizabeth's life."
He added: "People are looking forward to seeing the jets because we have been talking about them for flipping years. There's a lot of excitement on board."
Pilot in charge of jets: It's a new chapter
The pilot in charge of flight operations on the new carrier today said he is "massively excited" to see fixed-wing aircraft operating on the flight deck of HMS Queen Elizabeth.
Commander (Air) James Blackmore flew the last Harrier to take off from HMS Ark Royal in 2010.
He is now in charge of flight operations on board the Royal Navy's new carrier, which is about to undergo trials with the F-35B jets in the USA.
He said: "It's a full-circle process, it's great to be back here with the same captain, we are now working together again to bring jet aviation back to sea.
"It's massively exciting and this marks the start of the next chapter."
Describing the amount of preparation, Cdr Blackmore, whose position is affectionately known as "Wings", said: "This goes back almost to the point when we last finished jet flying at sea but, really, the last few years, since the ship came out of build and has been at sea, then we have been working hard as a team to get ready to bring an F-35 to the deck for the first time.
"Part of that was operating helicopters and understanding how the ship works, and we have also done a lot in simulators and working as a team with our US colleagues in the Integrated Test Force so we are ready to bring the jet to the deck in September."
Asked if he had any nerves about the process, he said: "Little bit, but I have got massive confidence in the team, certainly the team in my air department then collectively as a whole ship, we have all been working towards one common goal throughout the last couple of years, so everyone's focused, everyone's trained and we're ready to go."
Defence secretary Gavin Williamson said: "HMS Queen Elizabeth is a true statement of our national power and the whole country can be proud to see this magnificent symbol of our engineering prowess and international ambition leaving port to sail on to the world stage.
"Her voyage to America not only shows her global reach but strengthens our special relationship with the US forces who we have worked hand-in-hand with on this iconic programme.
"As she sails along the east coast of the USA, she will signal our determination to keep fighting alongside our allies in all corners of an ever more complex and uncertain world."
The honour of landing the first of the training jets on to the carrier will go to one of three British pilots taking part in the US deployment.
They are a Royal Navy commander, a RAF squadron leader and a civilian test pilot accompanied by a major from the US Marine Corps.
Facts and figures about the F-35B fighter jets on board
- The jet measures 51.2ft (15.6m) in overall length, has a wingspan of 35ft (10.7m) and a height of 14.3ft (4.36m).
- It has a top speed of 1.6 Mach or 1,200 mph, a Max G rating of 7G, and a combat radius of 518 miles (833km).
- Lockheed Martin, the American company building the jet, describes its stealth capabilities as "unprecedented". Its airframe design, advanced materials and other features make it "virtually undetectable to enemy radar".
- Britain has committed to a £9.1 billion programme to buy 48 of the jets by 2025 - with a pledge to purchase 138 - they will be jointly operated by Royal Air Force and Royal Navy pilots.
- The F-35B jets are built from more than 300,000 individual parts.
- The UK's supersonic aircraft have been based in the US since their manufacture.
- There are six distributed aperture system sensors around the jet - two underneath, two on top of the aircraft and one either side of the nose. These infrared cameras feed real-time information and images into the pilot's helmet, allowing them to see through the airframe.
- All variants of the jets are mainly constructed on Lockheed Martin's mile-long production line in Fort Worth, Texas.
- It takes 58,000 man hours to build each F-35B.
- The F-35 can launch from land, and will take off from HMS Queen Elizabeth via the skip jump ramp, which has been designed to optimise the launch.
- Maximum thrust tops 40,000lb and the jet has a range of 900 nautical miles.
- The jet is capable of two types of ship landing - vertically on to the deck, and also through the shipborne rolling vertical landing, which using forward air speed, allows the aircraft to bring back several thousand pounds of extra weight to the ship.
- The warplanes will carry out missions from the two Queen Elizabeth-class aircraft carriers - HMS Queen Elizabeth and HMS Prince of Wales.
- Lockheed Martin said across the 3,000 jets being built, 15% of each one is comprised of parts from British companies.
- Some of the UK companies with contracts to produce parts of jets includes Rolls-Royce, BAE Systems, Ultra Electronics, Selex, Cobham and GE Aviation.
- Lockheed Martin UK chief executive Peter Ruddock said that, to date, the F-35 programme has generated 13.5 billion dollars in contracts for British suppliers.
- HMS Queen Elizabeth weighs 65,000 tonnes and has a top speed of 25 knots, its flight deck is 919ft (280m) long and 230ft (70m) wide - enough space for three football pitches.
Commodore Andrew Betton, commander of the UK Carrier Strike Goup, said: "These first F-35B embarked trials in a UK aircraft carrier are not only key to future operational success but represent an iconic moment for the modern Royal Navy."
On leaving Portsmouth Naval Base, HMS Queen Elizabeth will carry out tests in UK waters before heading across the Atlantic to the US where as well as the tests, it will visit New York.
It will be joined by support ship RFA Tiderace and Plymouth-based Type-23 frigate HMS Monmouth as well as Merlin MK2 helicopters from 820 Naval Air Squadron, RNAS Culdrose, Mk 4 Merlins from 845 Naval Air Squadron, RNAS Yeovilton, and Royal Marines from 42 Commando, Plymouth.
The first of the UK's joint Royal Navy and RAF F-35B supersonic jets arrived from America in June and are based at RAF Marham in Norfolk.
Testing with these British aircraft is expected to take place onboard HMS Queen Elizabeth next year.
It has already undergone training with helicopters which have carried out more than 1,000 take-offs and landings.
The carrier is expected to embark on its first operational deployment in 2021.
Reporting by PA