WASHINGTON — The US Air Force's single biggest research program is also its most mysterious.

In the president's fiscal 2016 budget request, the Long Range Strike-Bomber (LRS-B) program is budgeted for $1.2 billion in research and development funding, making it the largest system under the Air Force's $17.9 billion research, development, test and evaluation (RDT&E) funding request.

RDT&E funding for the bomber will continue to escalate over the future years defense plan (FYDP), with a planned request of $2.2 billion in fiscal 2017, $2.8 billion in 2018, $3.6 billion in 2019 and $3.7 billion in 2020. Those figures do not reflect money that is hidden in the "black" budget as well, which could dramatically increase the cost of the program.

The LRS-B program is targeting a production line of 80-100 planes, with an estimated cost of $550 million each, although critics of the program warn that is not a realistic figure. It will eventually replace the fleet of B-52 and B-1 bomber fleets. Although technical specifications are largely unknown, it is expected the design will be stealthy, with optionally manned capability .

A down-selection will be made this spring or early summer, with initial operating capability planned for the mid-2020s. Nuclear certification will follow two years after that.

After the bomber comes the KC-46A tanker at $602 million requested and the F-35A engineering, manufacturing and development (EMD) phase at $589 million. Unlike the bomber, those RDT&E funding profiles will likely track down, as both those programs are close to going operational. The F-35A goes operational in 2016, with the KC-46A in 2017.

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Following that is the GPS III-OCX ground station program, a contract awarded to Raytheon, at $350 million, then the Space-Based Infrared System (SBIRS) EMD phase at $292 million and the Advanced Extremely High Frequency (AEHF) system at $228. The costs of those three space programs aligns with what Gen. John Hyten, the head of Space Command, has been saying about needing to drive down the development costs of satellite systems.

Science and technology accounts receive a $2.3 billion request, at a time when the service is emphasizing scientific development as a way to keep up with growing high-end threats from nations such as China.