A letter to be sold reveals a senior officer had a "queer feeling" about his posting to the ship.
Today`s auction in Devizes is one of the biggest involving Titanic memorabilia for many years.
RMS Titanic had been four days into a week-long Transatlantic crossing from Southampton to New York when the supposedly "unsinkable" ship struck an iceberg on 14 April 1912.
The ship sank less than three hours later at around 02:20 on 15 April. More than 1,500 passengers and crew were killed.
The letter is part of a collection, written over a 20-year period by Chief Officer Henry Wilde, who was second in command to the ship`s skipper, Captain Edward Smith.
Chief Officer Wilde was expecting to take command of another ship, the Cymric, and only signed onto the Titanic on 9 April 1912, the day before the ship sailed.
On 31 March 1912, he said he was "awfully disappointed to find the arrangements for my taking command of the Cymric have altered. I am now going to join the Titanic until some other ship turns up for me".
In another letter to his sister, written onboard Titanic and posted at Queenstown (now Cobh) in Ireland, he indicated he had misgivings about the new ship.
"I still don`t like this ship... I have a queer feeling about it," he wrote.
After the collision, Chief Officer Wilde took charge of the even-numbered lifeboats, and oversaw their loading and lowering into the water.
Auctioneer Andrew Aldridge, of Henry Aldridge & Son, said: "It is without doubt one of the finest Titanic-related letters, written by one of the liner`s most senior officers on Olympic stationery.
"This lot reveals previously unknown details and shows Wilde`s obvious disappointment in being transferred to Titanic.
"What is certain is that he worked diligently to load the boats once the seriousness of the situation was clear to him."
Rare photos of Capt Smith could sell for £1,000 each, the auction house has estimated.
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