Comparing roles: how the USAF uses its largest cargo planes

In terms of cargo capacity, the C-5 Galaxy leads with an ability to carry up to 270,000 pounds (122,500 kg) of cargo—including M1 Abrams tanks or CH-47 Chinook helicopters—using both upper and lower decks. The nose can be raised for loading through both ends. The C-17 carries less—around 170,000 pounds (77,500 kg)—but offers modularity for various missions such as troop transport or medical evacuation. It also supports aerial delivery via its rear ramp.

Physically, the Lockheed C-5 Galaxy measures over 247 feet in length with a wingspan of nearly 223 feet. It stands at 65 feet tall and has an upper deck running along its fuselage length. In contrast, the Boeing C-17 is smaller at 174 feet long with a wingspan just under 170 feet and a height of about 55 feet.

Data from WebFlite shows that while the C-5’s size limits it to larger bases with substantial infrastructure, the more compact dimensions of the C-17 allow it access to smaller airfields.

Both aircraft cruise at about 450 knots (520 mph). The service ceiling for the C-5 is approximately 35,000 feet; for the C-17 it is higher at around 45,000 feet. Crew requirements differ as well: "The C-5 typically requires a flight crew of seven: two pilots, two flight engineers, and three loadmasters," whereas "the C-17...can be operated by a crew of just three: two pilots and one loadmaster."

Runway performance also distinguishes these planes. According to AeroCorner data referenced in the article, "the C-5...typically requires around 8,300 feet (2,530 meters) of runway for takeoff at operational weights," while landing can require as little as 2,600 feet (792 meters). The "C-17 has been optimized for tactical flexibility and can take off in as little as 7,600 feet (2,316 meters) and land in just 3,500 feet (1,067 meters), sometimes less depending on weight and conditions."

While both can land on poor surfaces if needed, only the C-17 is designed specifically for short-field operations on unprepared runways.

Despite surface similarities as heavy-lift cargo aircraft within US Air Force operations worldwide https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104492/c-5-galaxy/, their roles are complementary rather than competitive. The article notes: "Rather than being redundant...these aircraft work in tandem to create a layered and responsive logistics system." The combined capabilities enable effective responses ranging from combat deployments to humanitarian aid.

This division ensures that US military airlift remains adaptable amid changing operational demands worldwide.