They will spend up to four hours looking at the bow section of the ship, the boilers and one of the propellers.
"The first time I saw it was awesome," McCallum said. "There's a moment in every expedition when you see what you came for and it's 'wow' - emotional. All the hard work and effort you've gone to has suddenly paid off."
He was struck by the size of the Titanic and its new inhabitants. "When you look out a porthole 4km underwater and see life, that's pretty special, as well. It's pitch-black, frigid and yet there's life there."
McCallum said the people who went on the dives were surprisingly average. "Nurses, teachers, journalists ... people who are captivated by whatever captivates them. But they think hard about what they are going to do because it costs a lot of money."
Stairway to history
Mary Gould will never get the chance to dive to the seabed to see the magnificent staircase her grandfather built for the ballroom of the Titanic.
But with the release of the movie in 3D this month, the Aucklander hopes to at least get a decent impression of what it might have looked like in all its glory.
Gould's grandfather and uncle worked on the construction of the Titanic at the Harland and Wolff shipyards in Belfast.
Her grandfather crafted the magnificent staircase into the ship's grand ballroom, before he moved to New Zealand to work as a carpenter on the railways in the 1920s.
"He was proud of it, of course," said the Pt Chevalier woman. "The family is proud of it."