More details on Boeing’s new T-X trainer should be unveiled Tuesday, a week before the Air Force Association’s annual Air, Space and Cyber Conference outside Washington, D.C.

For three years, Boeing has been secretive about its proposal to manufacture the new twin-engine, supersonic jet trainer. The Chicago-based company, collaborating with Saab, is directly competing with Northrop Grumman Corp. for a new “clean sheet” design.

The Air Force wants a replacement for its T-38 Talon trainer aircraft, first produced by Northrop in 1959. The Talon is used to prep pilots for “front-line fighter and bomber aircraft such as the F-15E Strike Eagle, F-15C Eagle, F-16 Fighting Falcon, B-1B Lancer, A-10 Thunderbolt and F-22 Raptor,” according to the service.

The service hopes to buy 350 new trainer jets.

Photos surfaced last month on social media showing the Northrop version of the aircraft. Northrop spokeswoman Katherine Thompson confirmed to Defense News that the photos were of its trainer, which was conducting taxi testing in Mojave, California. Northrop is partnering with BAE Systems, L-3 and Rolls-Royce on the project.

Promo videos of Boeing’s version were posted on the company’s site days after Northrop’s flightline tests. The official Twitter account for Boeing on Sept. 1 also posted, “Mark your calendars: #NewBoeingTX will be revealed in St. Louis on September 13” with a link to the sneak peek videos.

Other vendor teams such as Lockheed Martin Corp. and Korea Aerospace Industries, and Raytheon Co., Leonardo-Finmeccanica and CAE Inc. are offering modification designs to current aircraft, but are not competing in clean sheet designs.

At the upcoming AFA conference, Boeing will have five exhibit booths on the technology show floor, more than any other defense company presenting at the exposition.