One of its defining capabilities is the ability to operate from relatively short and austere airfields.
That capability made it ideal for Keiko's journey.
The U.S. Air Force later described the C-17 as the only aircraft capable of carrying such a large load directly to the short, remote runway on the Westman Islands.
This was not a donation of military flying time in the casual sense.
The Free Willy Keiko Foundation paid the Air Force for the transport.
Contemporary reports placed the cost of the overall relocation at around $2 million, with hundreds of thousands of dollars associated with the military flight itself.
The mission required extensive planning.
This was an animal who had become famous around the world.
Every stage of the operation had to account for Keiko's health.
Jeff Foster, who directed field operations for the foundation, told CBS before the mission that planners had considered an enormous range of contingencies—from medical emergencies to unexpected diversions.
There would be little room for improvisation once the whale was airborne.
September 9, 1998
The departure became a public event.
On September 9, Keiko was guided from his large aquarium pool into a smaller medical area where handlers could prepare him for transport.
A nylon sling was positioned around his body.
He was carefully lifted into his custom transport container.
The tank was then moved by truck from the Oregon Coast Aquarium to Newport Municipal Airport.
Hundreds of people gathered along the route.
CBS described crowds lining the road to say goodbye.
For residents of Newport, Keiko had become much more than an aquarium attraction.
For more than two years they had watched him recover.
Now they were watching him leave.
At the airport, the unusual cargo was transferred to the waiting C-17.
Air Force loadmasters faced a mission unlike almost anything in a standard military manual.
Inside the cargo bay was a living marine mammal weighing more than four tons.
The transport container had to remain secure.
Water movement had to be controlled.
Keiko's condition had to be continually monitored.
Veterinarians and foundation personnel stayed with him throughout the journey.
Then the C-17 took off.
Keiko was heading east.
Back toward Iceland.
The Flight Across the Atlantic
Contemporary accounts differ slightly on the exact flight duration, generally describing it as approximately eight to nine hours.
The journey was direct to the Westman Islands, although the C-17 received aerial refueling during the mission. Reports from the Keiko project described two midair refuelings during the transatlantic flight.
Inside the aircraft, Keiko remained in his water-filled transport system.
Three veterinarians and several trainers reportedly accompanied him.
Despite the extraordinary circumstances, the whale handled the journey well.
This was important because the flight itself was only one part of a much longer transport operation.
Once Keiko landed, he still needed to travel from the airport to the harbor.
Then he would be placed aboard a barge.
Only after that could he be carried to his new sea pen.
The operation was approaching its most dangerous logistical moment:
Landing.
The C-17 Reached Vestmannaeyjar
On the morning of September 10, the Globemaster descended toward the airport on Heimaey, the largest of the Westman Islands.
The runway was short compared with the large bases where military cargo aircraft commonly operated.
That was precisely why the C-17 had been selected.
The aircraft touched down.
Keiko had reached Iceland.
Then something went wrong.
Later reporting from Air & Space Forces Magazine, summarizing the Air Force accident investigation, said the right main landing gear failed during the landing.
The cause was traced to a design issue and metal fatigue associated with a component of the landing gear.
The aircraft sustained substantial damage.
But the most important fact was simple:
Nobody was injured.
Not the crew.
Not the animal-care team.
And not Keiko.
The whale had just crossed the Atlantic inside a military cargo aircraft and survived a landing-gear failure at the end of the journey without injury.
His trip was not over.
Back Into Icelandic Seawater
After the C-17 landed, Keiko's transport container was unloaded.
He was moved from the airport toward the harbor and then carried by barge to his new home.