Air Force One is easily the most well-known plane in the world. But the term "Air Force One" doesn't apply to one specific plane: It's the official military call sign for any US Air Force plane carrying the president.
Since 1990, two nearly identical (and heavily modified) Boeing 747-200B airliners have transported US presidents and served as airborne command centers during times of crisis. The pair were expected to be replaced by 2024, but criticism from President Trump over costs has put these plans in doubt.
Here's everything you need to know about the president's personal airplane -- and its future.
The cost to operate Air Force One in fiscal 2016? More than $180,000 per hour. And that's not counting the $325 million the US government paid for each plane.
The hourly cost includes more than just staff and fuel. The plane must be constantly guarded and housed in secure locations, and a backup must always be ready within 30 miles of wherever the president flies.
Air Force One is also subject to near-constant maintenance, which includes a full exterior waxing...by hand.
Air Force One looks like a standard Boeing 747, but only on the outside.
Inside, Air Force One has the specialized electronics and communications equipment (with roughly 238 miles of wiring), all heavily shielded, needed for the president to maintain constant contact with government officials on the ground.
"It really is, in many ways, a flying White House," Air Force Secretary Deborah Lee said.
President Trump took his first trip on Air Force One on January 26, 2017, when he flew from Andrews Air Force base, in Maryland, to Philadelphia for a meeting with Republican lawmakers.
Trump's opinion? "Beautiful. Great plane," he said.
In fact, the nose of Air Force One is often referred to as the "White House" of the plane. It contains the president's executive suite with bathrooms and fold-out couches. The southwestern theme for the room was designed by former first lady Nancy Reagan.
In this photo, President George W. Bush chats with Chief of Staff Andrew Card in the plane's executive suite in the hours following the September 11, 2001 terrorist attacks.
The front of the plane also contains this, the president's private office. It has been upgraded with the telecommunications equipment needed to conduct business as if the president were in the actual White House.
This infrastructure was added post-9/11, after President Bush was forced to land Air Force One at Barksdale Air Force Base in Louisiana to address the nation.
On his first trip aboard Air Force One, President Trump allowed the press inside his office for a photo opportunity. There, he compared the taxpayer-funded plane to his own personal 757.
"That's a good one too but this is a very special plane for a lot of reasons," he said.
Air Force One has a medical compartment that doubles as offices near the president's quarters in case of emergency. It has a supply of prescription drugs, a defibrillator, and a store of blood for in-air surgery. A nurse is also present on all flights.
Here, presidential nurse Cindy Wright comforts President George W. Bush shortly after the terrorist attacks of 9/11.
If you walk toward the back of the plane from its main entrance, you'll wind up passing through here, the Air Force One conference and dining room.
The food served on Air Force One goes well beyond usual airline fare.
Meals for the president, staff and guests are prepared by military chefs at Joint Base Andrews in Maryland. Food is partially cooked, vacuum sealed and frozen on the ground. Meals are finished aboard the plane in one of two galleys.
Hallways run down the sides of the plane, lined with armored windows.
With about 4,000 square feet of interior space, the nearly 232-foot-long Air Force One is surprisingly spacious inside.
Walk even further toward the back of Air Force One and you'll pass through here, the staff quarters. The area has 85 color-coded phones (white phones are standard lines; beige phones are secure lines) and 19 televisions.
Air Force One has 14 seats for reporters in the rear of the plane. Journalists have the freedom to walk toward the back of the plane while in flight, but the Secret Service prohibits them from walking forward past their own seat.
Guests get a few basic souvenirs, such as matchbooks and a first-timers' certificate, but no one rides for free. Reporters are required to reimburse the government for the cost of a seat on a similar commercial flight.
Here, White House spokesman Sean Spicer talks with the press aboard Air Force One during President Trump's inaugural flight on January 26, 2017.
No tour of Air Force One would be complete without a visit to its cockpit, located directly above the president's private quarters.
The cockpit is slightly roomier than those on commerical airplanes.
One of the biggest differences between Air Force One and a standard Boeing 747: The former comes ready for midair refueling by a plane such as the KC-135R Stratotanker, shown here.
The president's plane can easily stay in the air for a week or more at a time, but due to the dangers of the refueling maneuver, such an event would only occur in a crisis.
Boeing is currently under contract to design a pair of new Air Force One planes by 2024 based on the company's new 747-8 model, seen here. The new plane is longer (250 feet, 2 inches versus 231 feet, 10 inches), faster (0.855 mach versus 0.84 mach), and has better range (7,730 miles versus 6,735 miles) than the current design.
It also has a smaller environmental footprint, emitting 16 fewer tons of carbon dioxide per trip.
The final price tag for the two replacement planes is expected to fall between $3 billion and $4 billion, though President-elect Trump is working with Boeing to reduce costs.
There have been reports that Trump may prefer to fly in this, his own personal 757 jet, rather than Air Force One. But that's unlikely. Trump's plane may be more comfortable and contain more gold-plated items (including the seatbelts!), but it lacks the upgrades needed to keep the leader of the free world safe.
Even if Trump did fly in his own plane, it might not save the taxpayer any money. When Vice President Nelson Rockefeller chose his own personal aircraft over Air Force Two, it actually cost more money to provide separate flights for his security team and staff.
Air Force One has seen more than its fair share of US history.
White House photographer Cecil W. Stoughton took this, arguably the most iconic photo aboard Air Force One in American history, at 2:38 PM on November 22, 1963, following the assassination of President John F. Kennedy in Dallas.
Stoughton said the photo of President Lyndon B. Johnson being sworn in next to a still-bloodied Jacqueline Kennedy is "tasteless," but noted the "history-making moment" was too important to US history for it not to be documented.
President Dwight Eisenhower and first lady Mamie Eisenhower disembark the Columbine II, the first plane to be given the call sign "Air Force One." It entered service in 1953 and was replaced by the Columbine III in 1954.
The plane was used to carry other VIPs until it was retired by the US Air Force in 1968 and sold to a private buyer in 1970. This makes it the only Air Force One to ever be owned by a civilian.
The initial private owner of the Columbine II was, at first, unaware of the plane's presidential heritage. He had intended to convert it to a crop duster, but, thankfully, decided to use it for parts instead.
In 2015, the plane was sold to Dynamic Aviation founder Karl Stoltzfus, Sr., who promised to complete a restoration of the historic airliner which, as you can see, the plane is in sore need of.
Though Eisenhower was the first president to fly on Air Force One, he certainly was not the first president to fly. That honor goes to Theodore Roosevelt, who flew in a Wright exhibition plane on October 11, 1910 during a campaign event for the Missouri State Republican Party.
The first president to use a plane for official business was Franklin D. Roosevelt, who made a four-day, cross-Atlantic journey in 1943 to hold a strategy meeting with Winston Churchill in North Africa. The flight was very risky, but advisors believed the proliferation of German U-boats made travel by sea even riskier.
What happens when an Air Force One plane gets retired? SAM 27000, which served presidents Nixon through George H.W. Bush, was retired from regular presidential service in 1990. It was retained as a backup through 2001.
The historic plane was eventually secured by the Reagan Foundation in Simi Valley, California. It's now on display at the Ronald Reagan Presidential Library and Museum, where it was used as a backdrop during a Republican presidential primary debate in 2015.
Finally, there's more than one way for a president to travel the skies.
The Marines maintain and keep ready a Sikorsky SH-3 Sea King helicopter, named Marine One, to ferry the president and his guests on shorter trips and to areas a large plane cannot easily land.