The Glock 21 is Glock's full-size .45 Auto service pistol family. The cataloged G21 SF reduces the receiver circumference for smaller hands, the Gen4 adds modular backstraps and a reversible magazine catch, and the Gen5 MOS adds optic mounting. In 2017, U.S. security assistance supplied 200 to Philippine Marines for Marawi.
The United States supplied 200 Glock 21 pistols to the Philippine Marine Corps in June 2017, with Philippine Marine leadership saying Marawi troops were the priority recipients during the 2017 Battle of Marawi.
GLOCK's own product pages show how the family changed across the SF, Gen4, and Gen5 MOS variants.
| Variant | What changed | Reader note |
|---|---|---|
| G21 SF | Short Frame design reduces the receiver circumference. | Built to improve ease of use and control, especially for shooters with smaller hands. |
| G21 Gen4 | Modular Back Strap system and reversible magazine catch. | Lets the grip and controls adapt to different hands and handedness. |
| G21 Gen5 MOS | Optic-ready slide, nDLC finish, ambidextrous slide stop lever, and Modular Backstrap System. | Adds a more modern, optic-capable layout for the .45 Auto family. |
GLOCK identifies the G21 Gen4 as chambered in .45 Auto, and SAAMI recognizes 45 Automatic as the correct cartridge name.
| Compatible item | Item type | Compatibility evidence |
|---|---|---|
 | Pistol cartridge | The G21 Gen4 is chambered in .45 Auto, which SAAMI recognizes as 45 Automatic (45 Auto). Sources: GLOCK 21 Gen4, SAAMI FAQs |
GLOCK's history page says the Gen4 era began in 2009 with multiple backstraps, a reversible magazine catch, and new frame texturing; the G21 Gen4 applies that update to the .45 Auto pistol family.
Sources: GLOCK history, GLOCK 21 Gen4
GLOCK says the Gen5 generation began in 2017; the G21 Gen5 MOS adds optic mounting, an ambidextrous slide stop lever, the Gen5 frame texture, and the Modular Backstrap System.
Sources: GLOCK history, GLOCK 21 Gen5 MOS
U.S. security assistance supplied 200 Glock 21 pistols to the Philippine Marine Corps, and Marine leadership said Marawi troops were the priority recipients during the battle.
Sources: Gov't troops in Marawi to receive new weapons, equipment from US, New weapons from US to be used by PH Marines in Marawi
