The royal couple have been given a personal tour of the Omaka Aviation Heritage Centre's collection of vintage planes by Sir Peter Jackson.
Royal watchers have migrated to the Centre for the second stop of Prince William and Catherine's stint in Marlborough.
Wet weather, which held off for this morning's ceremony at Seymour Square, failed to dampen the crowd's enthusiasm, which cheered as Kate and William arrived.
The pair were greeted by Sir Peter.
More than dozen aeroplanes from World War 1 and World War II were wheeled out of their Omaka Aviation Heritage Centre hangars in preparation for the royal couple's visit.
The Duke and Duchess were wowed when they entered the world-renowned museum.
A 26 foot-long grey WWI relic, a Caproni CA 22, greeted the royal pair for the start of the tour by Sir Peter Jackson.
"Oh wow, look at this!'' said an apparently impressed Prince William.
"This is awesome. How old is this?''
"1913,'' Sir Peter said.
Kate let her husband go ahead with the director while she walked with centre chief executive Jane Orphan.
Prime Minister John Key was also taking a keen interest.
Sir Peter, wearing a double-breasted jacket and tan trousers, strolled around his prize exhibits with a hand in his pocket, reeling off historical facts and insight.
Prince William, a pilot, was full of questions, becoming animated with the WWI and WWII planes hanging from the ceiling.
Kate soon joined in with the unique personalised tour.
The royal couple then disappeared from sight as Sir Peter continued the tour.
They then emerged to be greeted by World War Two Spitfire pilot Harcourt "Bunty" Bunt.
The 93-year-old from Picton explained the story of New Zealand's highest scoring ace of The Great War, Lt Keith Logan 'Grid' Caldwell.
Sir Peter left it to Bunty to explain the "Boyzone" story.
The couple listened intently to the amazing war tale.
Caldwell got into trouble behind enemy lines.
At 5000-feet he stepped out onto his wing - a fact that amazed the couple - and hung on to wing to control the plane and jumped off.
"He brushed himself off," and made contact with trenches, Bunty said.
"No way, that's amazing," William said.
"And how fast was he going when he jumped off?"
Sir Peter explained how he might've done it.
Kate added: "That's an extraordinary story."
She asked if he told his story while he was alive, to which her husband added: "He probably dined out on it for some time."
Bunty went on tell his life story. The royals were deeply interested in the tale and thanked Bunty for sharing it.
They were also shown the remarkable life-like exhibition of the infamous Red Baron's last flight when he was shot down over British lines and killed in 1918 - after a record 80 planes brought down.
Sir Peter explained that Australian troops were first on the scene and they proceeded to strip the plane for mementoes. It was a fact that brought a chortle from the prince. He wondered where the paraphernalia was now.
Sir Peter explained how they got the scene historically accurate, even down to the Somme field of mud it landed in.
William showed insight by noting the reason why so much is known about the crash scene is from those Australians.
At the end of the 30-minute tour, the Duke and Duchess had a brief look in the gift shop, full of scale plane models.
In a short presentation, Omaka Aviation Heritage Centre gifted Prince George a tiny vintage flying helmet.
"Oooh," the princess cooed when she opened it.
"That's brilliant," she added, thanking the centre.
The helmet was made by Trevor Lamb, using deer leather and has been custom dyed and finished, with a lining of New Zealand possum fur, Ms Orphan said.
The couple were then taken outside where several of the antique planes were lined up in mild drizzle.
The flying prince then sat in the cockpit of a Sopwith Pup biplane.
"It's perfect. Start her up," he said.
Graham Orphan showed the pair, under umbrellas with worsening damp, to several more planes.
A large waiting crowd clapped and cheered as they strolled around.
"I love you," one young girl called out.
The royal couple also stepped inside an Avro Anson plane from WWII, complete with rear gun turret.
Plane owners Bill Reid and his wife Robyn told them it took ten years to restore the plane - the only kind of its type.
William sat at the controls for some time, amazed with the cockpit controls, all from the war period, painstakingly restored.
Sir Peter, a benefactor of the Omaka Aviation Heritage Centre trust, said it was great to have the royal couple at the museum.
Prince William, who is an avid flyer, asked plenty of questions throughout the tour, he said.
"It nice, very, very nice," Sir Peter said.
In the couple's final moments of their visit to the centre, Sir Peter and Prince William could be heard joking about flying in New Zealand.
"I don't know what the paperwork is," Sir Peter said to the Duke.
A special touch was when 9-year-old Tallulah Dabinette was pulled out of the crowd to meet the royal couple.
She was holding a framed photograph of her as a 7-month-old baby meeting Prince William during a 2005 visit to New Zealand.
Along with sister Eloise, 7, and mother Sara-Lee, they met the Duke and Duchess and gifted them the picture.
"Thanks very much, it's very special,'' a touched Prince said.
He and his wife joked about "what age does'' and thanked them again.
Afterwards, all of three of them were blown away.
Tallulah, who goes to nearby Fairhall School, said the experience was "so cool''.
Ms Dabinette said the royals remarked on the acorns embedded in the wooden picture frame, saying that acorns were ``very special'' to them as they feature of their coat of arms.
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Earlier today, the royal couple arrived at Seymour Square 15 minutes after their 11am scheduled time.
Children hoping to see the glamorous pair sat on top of their parents' shoulders, while other people chose to take a perch in some of the larger trees around the square.
The duchess wore a blue Alexander McQueen coat, clinched at the waist with pleats at the back.
Her husband had war medals displayed on the left lapel of his navy suit jacket.
High pitched shrieks and yells of delight welcomed the couple to Seymour Square.
Cameras and mobile phones were hoisted high above the heads to capture a regal peek.
One couple standing on step ladders called out "Who's laughing at our steps now?".
The royal couple met 10 veterans and paid their respects to the fallen World War one soldiers.
The Last Post echoed round the park.
The RSA ode was read in Maori and in English by Staff Sergeant Paul Whakatihi of the Royal New Zealand Infantry Regiment reserves and Marlborough RSA Vice President Rod Shoemark, respectively.
Marlborough Girls' College Year 12 students Olivia Burns and Alice Schofield sang the national anthem as a helicopter droned overhead.
World War II veteran Wilton Sterritt was one of 10 serviceman who met the Duchess today.
"Just beautiful,'' he said.
Mr Sterritt, who gave his age as over 90, brought a special photo to show the royal couple today.
The photograph shows a much younger Mr Sterritt with a relaxed looking Prince Phillip. Photo / Getty Images, Teuila Fuatai
"It's the Duke of Edinburgh at the [Christchurch] Commonwealth Games in 1974.''
The photograph shows a much younger Mr Sterritt with a relaxed looking Prince Phillip.
"I was on the organising committee [for the Commonwealth] games. I had to show him around all the shooting venues.''
While Mr Sterritt - who was a naval seaman - acknowledged the photo was a hit with Kate, he confessed to not being too aware of the conversation when asked what they discussed.
"I've got short memory,'' he laughed.
Crowds clamour for glimpse of royals
Isla Read, 7, was left trembling with excitement after the princess accepted a bouquet of flowers from her.
"My legs are shaking," the Springlands School Year 3 pupil told her mum, Moira Maher.
Isla told the Duchess: "Nice to meet you.''
Kate, who took her time shaking hands and exchanging pleasantries with the adoring fans, replied: "Nice to meet you too."
She then thanked her for the bouquet of lilac posies.
Ms Maher said: "It's really exciting for Isla. It'll be something to remember the rest of her life."
They watched the royal wedding three years ago and were delighted to see them in the flesh.
"It's very special - and great for the town."
Ayla Simpson, 11, arrived at 6.30am to snatch up one of the prime positions at the square.
"There were only four other groups of people here, not this many," she said, excited.
Ayla, who is from Blenheim, was the first of her four friends to arrive.
The group hung a flag of the Duke and Duchess over the barrier in front of them, and had also made paper crowns for the occasion.
"It's cool, we're only here once."
Also in the crowd was Sally Small.
Miss Small and her friends had brought deck chairs and biscuits for the wait.
"We got here at 8am.
"We're here to see the royal couple".
Many people are wearing the red, white and blue of Britain and many are waving Union Jack flags.
Lynda Day, 64, and Veronica Dugdale, 68, have come from Motueka for the day.
"It's very exciting, isn't it," Mrs Day said.
Seeing Kate was the main event for her.
But Mrs Dugdale, originally from England, especially wanted to see William.
"I remember when Diana was laid to rest and how huge that was," she said.
She is disappointed that she won't see baby George, though.
"It's a shame Kate isn't taking George more places, especially since Diana took William everywhere. I guess I shouldn't compare generations."
Earlier today, Marlborough's mayor Alistair Sowman said the occasion was particularly significant for veterans.
About 100 servicemen and women have been invited to the commemoration.
Mr Sowman told Newstalk ZB the day is a chance to join the royal couple in commemorating 100 years since the outbreak of World War One.
The commemoration will be followed by a visit to the Omaka Aviation Heritage Centre, where film director Sir Peter Jackson will give the royals a personal tour of his private plane collection.
William and Kate's day will conclude with meetings with Prime Minister John Key and Labour leader David Cunliffe, and a state reception at Government House.
Marlborough Girls College students Isabella Chaytor-Waddy, Georgia Lee, and Rose Asriamah - all aged 15 - were delighted to see some celebrities come to town - and get some time off school.
"No one ever comes to Blenheim so we're pretty excited to see the royals," Miss Chaytor-Waddy said.
And Miss Lee added: "Especially Will and Kate ... they're quite new. She's quite modern."
"It's just a shame baby George isn't here," Miss Asriamah said.
The Haydon family from Nelson, dad Shane, 21-month-old Edward, William, 5, Samuel, 3, and mum Sarah, have got into the spirit of the occasion.
Mrs Haydon, originally from England, says it's a day to support her homeland and to "feel very patriotic".
She's been planning all week, husband Shane said.
The kids even know how to do the "Royal wave".
"It's fantastic to be able to see them," Mrs Haydon says.
"We've taken kids out of school. We're doing to do a project for school too.
"William has been saying he's very excited to see Prince William."