An unprecedented second state visit to Britain by U.S. President Donald Trump was due to get underway when he and First Lady Melania Trump arrive later Tuesday.

President Donald Trump pictured in the Oval Office at the White House in Washington D.C., on Monday, a day before he was due to depart for London for a historic state visit, his second. Photo by Samuel Corum/UPI UPI

Sept. 16 (UPI) -- U.S. President Donald Trump was due to touchdown in Britain later Tuesday as he embarks on an unprecedented second state visit to the United States' closest ally as the guest of King Charles.

Trump and first lady Melania Trump will be met from Air Force One by Foreign Secretary Yvette Cooper, U.S. Ambassador to the U.K. Warren Stephens and Viscount Hood, King Charles' lord-in-waiting, before being whisked off to Windsor Castle, their main base for a packed schedule of events.

The visit gets underway in earnest Wednesday morning when the Trumps will be formally welcomed with a gun salute fired from the east lawn of Windsor Castle and the Tower of London, 25 miles away, simultaneously.

They will then ride a carriage through the estate in the company of the king, Queen Camilla, Prince William and Princess Catherine along a route lined with military personnel and music provided by the bands of the Royal Marines, army and Royal Air Force.

They will be greeted by a honor guard on arrival at the castle before lunch in the state dining room, followed by a tour of the royal art collection.

After lunch, the president and first lady will lay a wreath on the tomb of Queen Elizabeth II in St. George's Chapel, which is in the grounds of the castle, followed by a tour and a recital by the chapel choir.

Prime Minister Keir Starmer and his wife, Victoria Starmer, will join the group to view the "beating retreat," a military ceremony involving the beating of drums and parading of Post Guards that dates back to the 17th century, followed by a fly past of the Red Arrows and U.S. and British F-35s, weather permitting.

The main event, the state banquet, comes up on Wednesday evening, a traditional white-tie event at which the king and Trump will deliver speeches.

Trump will begin the final day of his visit on Thursday by traveling to Chequers, Starmer's country residence, 40 miles northwest of London.

This will be the business part of his visit, although there will still be a full honor guard complete with bagpipers -- a nod to Trump's Scottish roots -- when he is greeted by Starmer ahead of bilateral talks.

Afterward, they will host a reception with executives from British and American companies, including GSK, Microsoft and Rolls-Royce, followed by lunch, before wrapping up their mini-summit with a news conference at which they will announce deals on technology and financial services.

Investment in AI and super and quantum computing is expected to be the focus of the tech agreement.

While a second visit is unknown for a non-royal, it will differ from Trump's first visit in 2019 -- which attracted both large protests and controversy after he walked ahead of Queen Elizabeth and intervened in domestic politics -- in that there will be no public appearances or events.

He will not be able to address Parliament as Tuesday was the last day it sits before a month-long recess for party conferences.

At least one demonstration, however, is expected to be held on Windsor's main street on Tuesday.

Security will be tight across the three days the Trumps are on the ground, with British authorities expected to mount one of the largest ever operations for a visiting foreign leader with a price tag running into the tens of millions of dollars.