In 1985, while the U.S. military chose the Beretta 92FS, dubbed the M9, as the standard sidearm, the Navy SEALs later switched to the SIG Sauer P226 due to issues with the M9. The SEALs reported slide cracks and catastrophic failures in the M9s, leading to their removal from service. Despite the subsequent investigation finding the 9mm submachine gun ammunition, not the M9 itself, at fault for the failures, the SEALs continued with the SIG Sauer P226.
  

Key Points: 

1. In 1985, the U.S. military adopted the Beretta 92FS (M9) as the standard sidearm, replacing the M1911A1, and issued it across all service branches.
2. Despite the M9’s overall reliability in tests, the Navy SEALs reported issues with slide cracks and catastrophic failures during its use.
3. The SEALs switched to the SIG Sauer P226, a maritime version designated as the Mk25 Mod 0 after issues arose with the M9.
4. Investigations found the issues with the M9 were not due to the pistol itself but the higher pressure 9mm submachine gun ammunition used by the SEALs.
5. Despite the discovery, the Navy SEALs decided not to readopt the M9 and continued using the Mk25 until switching to the Glock 19 (Mk27).

Source: https://www.wearethemighty.com/tactical/why-the-navy-seals-chose-the-sig-sauer-p226-over-the-m9/