President John F. Kennedy arrives in Alameda, California on March 23, 1962. (JFK Presidential Library and Museum)

President George W. Bush tried to buy a new Air Force One before the end of his presidency, but was blocked. Inside the Pentagon, top generals could not agree on how many new aircraft to buy; some wanted three aircraft, others two.

There are two VC-25s now. One of the aircraft is typically in maintenance, a process that lasts about six months. But when the ever-expanding campaign season comes around, the White House often wants both VC-25s ready hit the trail, according to former Air Force officials associated with the plane.

Some within the Pentagon felt a fleet of three Air Force One aircraft would ease maintenance pressure and ensure two jets were always ready. Others felt that the Air Force should combine buying new presidential jets with the overdue replacement of the defense secretary’s plane, the E-4B Nightwatch, more commonly called the “Doomsday Plane.” The E4-B is a specialized 747 designed to serve as the command center in the sky during a nuclear war. There are four Doomsday Planes, all heavily modified 747-200s built for the military in the 1970s.

If the Air Force buys the planes in 2016, the earliest it would likely carry a president would not be until 2019.

At the time, a separate project to build a new Marine One, the president’s helicopter, was delayed and wildly over budget. In the end, everything was canceled, delaying the new Air Force One project at least six years.

Now as the 2016 budget proposal goes to Congress for review, it is the last opportunity to buy a new Air Force One for at least another five years. This will be the last budget the Obama administration crafts and executes. It will build a 2017 budget, but Obama’s successor will likely modify it upon taking the oath of office in January of that year.

If the new plane is not purchased now, the project would certainly be delayed indefinitely as a two-term president would be needed to make the buy.

And there is another reason why the Pentagon is running out of time to buy an aircraft. Boeing announced late last year that it would slow production of the 747-8, the most recent variant of the 747, which is much larger, more efficient and high-tech than VC-25 airframe.

The Air Force formally announced last week that the new Air Force One would be a modified 747-8, not a surprise since the only other candidate was the quad-engine Airbus A380, which is a gargantuan, two-deck super jumbo jet. Airbus had expressed little interest in the new Air Force One project as it had been viewed as a political dark horse for one major reason: The aircraft is built by the multinational, European company in France. Boeing – the only American wide-body aircraft manufacturer left in business after decades of consolidation – had been seen as the only option for the new presidential aircraft. And when it comes to buying an aircraft that will fly around the president of the United States, buying American really matters, experts and historians say.

In an attempt to control costs throughout the project, the Air Force is looking to compete long-term maintenance and upgrade work on the new jets over the 30 years it is expected to carry American presidents.

There is no formal delivery timeline for the new aircraft yet, but if the Air Force buys the planes in 2016, the earliest it would likely carry a president would not be until 2019 or 2020, experts say, as the specialized modifications will likely take two or three years.

While the 747 has been considered the most likely contender to fly the president, the Air Force could have gone with a smaller, twin-engine 777 aircraft, but experts say it was not a likely candidate for two reasons: First, the extra two engines on the 747 generate much more power for the special communications and electronic equipment. The other is ramp presence, or the plane’s ability to stand out against other aircraft on the flight line.

The president still flies on other military aircraft, which use the call sign Air Force One when he is on board, usually on short-distance flights or when an airport’s runway is not long enough for the VC-25. In those cases, the president would use a C-32, a modified Boeing 757, or a C-37B, an even smaller Gulfstream 550 business jet. The smaller planes do not have all of the bells and whistles of the larger 747.

With the new Air Force One project now moving along, the speculation can begin on who will be the president to christen it.