Typical return tickets of £800 will be more commonly available as low as £400, according to the airport’s chief commercial officer John Watson.
The news follows low-cost airline Norwegian announcing on Wednesday fares of around £200 when it launches US flights from the capital next spring. Mr Watson said the fares war would intensify because Delta will operate the biggest aircraft yet on the route this summer – with more seats to fill.
The twin-aisle Boeing 767-300, which will fly daily from June to September, has 210 seats compared to 163 in the single-aisle Boeing 757-200, which will launch the route and fly for the rest of the year.
United, which was first to operate the route in 2004, and American, which joined last year, both use Boeing 757s.
Mr Watson said: “You will see a much wider variation in fares, and at times they will be half current levels. All three airlines are nervous about each other, which is great.”
He said a larger aircraft on the route had been “long demanded” to provide more business class seats, which are regularly fully booked several days a week.
He said: “It will make a massive difference. I hope we will see a 767 all year round, and more than one flight a day.”
Mr Watson said the aircraft were also less prone to turbulence, helping nervous fliers, families and those trying to sleep.
Delta is returning to the route to John F Kennedy Airport which it scrapped in 2009.
However, Frank Jahangir, vice-president for sales in Europe, the Middle East and Africa, said his trump card was customer service, driven by staff receiving 20 per cent bonuses from its profits. He claimed: “We are one mile ahead of the competition in service.”
More than half of passengers are expected to be Americans, 45 per cent of those transferring to and from other flights at Delta’s JFK hub.