In terms of technical specifications, the two aircraft differ significantly. The C-5M is larger overall: it measures nearly 248 feet in length compared to the C-17's 174 feet; it also has a greater wingspan and height. The maximum takeoff weight for the C-5M is about 840,000 pounds versus 585,000 pounds for the C-17. In terms of payload capacity, the C-5M can carry up to approximately 281,000 pounds while the C-17’s limit is about 171,000 pounds. However, the C-17 is capable of operating from much shorter or unpaved airfields—a key advantage in forward or remote operations.

Operationally, both aircraft have demonstrated their value in different environments. During conflicts in Afghanistan and Iraq, C-17s were frequently used to deliver supplies directly to front-line or isolated locations thanks to their ability to land on short strips and reverse out using thrust reversers. Captain Fischer from Joint Base Charleston described a notable exercise where a single C-17 crew dropped over 2,300 paratroopers without needing intermediate stops.

The Galaxy remains essential for missions requiring transportation of extremely large or heavy items that cannot fit into other planes. Its dual-door system allows rapid loading and unloading of massive equipment such as tanks or helicopters.

Both aircraft have set records during their service lives. The C-17 reached its four millionth flight hour by early 2021—one of the fastest rates among military transports—and can carry an M1 Abrams tank when within weight limits. After upgrades through programs like AMP (Avionics Modernization Program) and RERP (Reliability Enhancement & Re-engining Program), the C-5M Super Galaxy set more than 86 aeronautical records.

Safety records show that fatal incidents involving these aircraft are rare but significant when they occur. In July 2010, a single fatal crash involving a C-17 occurred near Elmendorf Air Force Base in Alaska due to a stall at low altitude; all four crew members died. The most serious incident involving a C-5 took place during Operation Babylift in Vietnam in 1975 when a crash resulted in more than one hundred fatalities.

Economically, each aircraft presents different challenges for sustainment and modernization efforts. While expensive to produce—about $340 million per unit—the C-17 offers lower operating costs and higher mission-capable rates than its larger counterpart due largely to design choices that favor maintainability.

Currently, over 222 Globemasters are active globally compared with just over fifty modernized Galaxies remaining in service with the U.S. Air Force fleet.

Choosing between these aircraft depends on mission requirements: if size and distance are paramount—such as moving very large generators overseas—the Galaxy is preferred; if speed or access into restricted areas is necessary—such as disaster relief at small damaged airstrips—the Globemaster excels.

Looking ahead into 2025 and beyond, both models are expected to remain operational for years—with discussions underway about future platforms that might combine their respective strengths under initiatives like Next Generation Airlift (NGAL). Until then, they continue serving distinct but complementary roles within U.S. global air mobility operations.