United Airlines announced plans Thursday to buy 15 planes from airline startup Boom Supersonic in a move that could revive the high-speed form of air travel.

Under the commercial agreement, United would purchase Boom's "Overture" aircraft once the planes meet "United's demanding safety, operating and sustainability requirements" with an aim to start passenger travel in 2029, the companies said in a joint press release.

The agreement covers 15 planes and includes an option for United to obtain another 35 aircraft. The companies did not disclose financial terms.

Boom's plane is capable of flying at twice the speed of leading aircraft now on the market, with the potential to fly from Newark to London in three and a half hours and San Francisco to Tokyo in six hours, the companies said.

The jets will also be "net-zero" in carbon use because they will employ renewable fuel.

Commercial supersonic jet travel was introduced in the 1970s with the Concorde, but the jets were retired in 2003 due in part to the high cost of meeting environmental restrictions on sonic booms.

The Concorde's demise also followed a 2000 Air France accident that killed 113 people.

However, the technology is getting another look today as companies in the United States and abroad develop planes with lighter and more efficient composite materials and new engine designs, according to a fact sheet from the Federal Aviation Administration.

"Our mission has always been about connecting people and now working with Boom, we'll be able to do that on an even greater scale," said United Chief Executive Scott Kirby.

Founded in 2014, Denver-based Boom Supersonic said it is also working with the United States Air Force on a military version of the Overture.

Jon Ostrower, editor of the aviation publication the Air Current, said on Twitter that United's order marked a shift in a long-term industry trend.

"The last time United ordered supersonic aircraft, humans had yet to walk on the Moon," Ostrower said. "More than a half century later, United is again focusing on speed, bucking the most consistent airline trend over the past 50 years: a desire to fly cheaper, not faster."