The Ballydoyle trainer has won this Group Three race eight times since 2007, including the last five renewals, and has successfully used the mile-and-a-half contest as a stepping stone to the Investec Derby.
Ruler Of The World was successful on the way to glory at Epsom in 2013, while Wings Of Eagles lifted the Classic after finishing second to stablemate Venice Beach 12 months ago.
Hunting Horn is the likely first string of O’Brien’s trio, who all hold entries in the Investec Derby, and has had the benefit of two runs last month.
After making a successful reappearance at Naas, the son of Camelot was third to Sevenna Star in the Sandown Classic Trial.
He will be accompanied by Flag Of Honour, who was third in the Prix Noailles on his return last month, and Family Tree, winner of his sole start at Gowran in September.
O’Brien said of Hunting Horn: “He’s a horse that ran well in Sandown, so we’ll see how that goes.”
Hunting Horn is opposed by an old adversary in Ispolini, who was a length and a quarter ahead of him when beaten a short head by Sevenna Star at Sandown.
I was very pleased with Ispolini’s seasonal debut at Sandown and he looks to have come on for that race,” Charlie Appleby said.
“The step up in trip to a mile and a half will suit him and he should be competitive.”
Proschema has made a bright start to the campaign, winning in good style at Doncaster and trotting up by 11 lengths in a four-runner affair at Haydock.
Trainer Tom Dascombe reports the Declaration Of War colt to be in great condition and is looking to see if he warrants a crack at the Derby.
“He comes back after running only last week, but he seems in great shape,” said Dascombe.
It will be the quickest ground he’s ever run on, but it shouldn’t be a problem.
“We’ll just find out if he’s good enough. He’s done nothing wrong.”
Andrew Balding is throwing Perfect Illusion in at the deep end after winning both his starts in ordinary company at Lingfield during the winter.
However, Balding has faith in the son of Nathaniel, who has no stamina doubts as his victories came over a mile and a half.
He said: “It’s a little bit difficult to truly asses the merit of that form, but he’s a horse we’ve liked at home and he stays well, which is a plus.
“It looks a strong Chester Vase opposed to normal years. It looks a deep one for horses with chances and I just hope he runs well.”
William Haggas saddles a promising type in Young Rascal, who earned a tilt at Group-race level by winning a 20-runner maiden at Newbury by five lengths last month.
Mark Johnston’s Dee Ex Bee shaped encouragingly on his reappearance when third to Crossed Baton in the Blue Riband Trial at Epsom.
The Charlie Hills-trained Jetstream, who got off the mark at Newcastle in February, and another Irish raider, Miles Christianus from Robbie Osborne’s stable in Naas, complete the field.