Notes: At first known as the I-Max 100, this weapon is built by Singapore and used by that country, Croatia, and other "unnamed countries." It is highly resistant to dirt, is very light, and is well known for reliability. The stock can be removed (but not folded) and the weapon has a foregrip for control. The 20-inch barrel is of the quick-change-type and is tipped with a flash suppressor similar to that of the M-16 series. The Ultimax 100 has a folding carrying handle attached to the barrel at the weapon’s center of mass; this handle is also used when changing the barrel. The front sight is a protected post, while the rear is a protected aperture; both are adjustable for windage and elevation. The Ultimax may be fired only on automatic, but the cyclic rate of fire is so low (400-600 rpm, depending upon the setting of the gas regulator), that single shots may be easily squeezed off with only a minimum of practice. The folding bipod is simple, but not adjustable, and can easily be removed if desired. Construction is largely of light, strong steel, light alloys, and polymers, making the Ultimax 100 very light.

The Ultimax 100 Para is a short assault version of the Ultimax 100. The barrel is shorter at 13.1 inches, and the butt is normally removed, though a sliding or fixed stock may be attached. It is otherwise the same as the standard Ultimax 100. An even shorter-barreled version, the Mk 3, is also available, basically making the Ultimax into an assault carbine; this version also is normally encountered with a sliding or removed stock, and uses a 10.5-inch barrel. The Ultimax 100 Mk 3 does not normally mount a bipod, but one may be mounted if desired.

Normal feed for all of these Ultimax 100 variants is from 20 and 30-round M-16 magazines, 35 and 50-round magazines of the type designed for the Galil, and a proprietary 100-round drum. A variant series called the Ultimax 2000 can use these magazines as well as any NATO STANAG-compatible or Israeli 5.56mm magazine. The Ultimax 2000 comes in the same versions as the Ultimax 100, and is otherwise identical for game purposes as the Ultimax 100.

In 2005, the US Marines, dissatisfied with the M-249 SAW’s numerous shortcomings and defects, began to look for a replacement; they also wanted something lighter than the SAW. Though as of late 2006, the final determination has yet to be made, but the Marines seem to be especially enamored of a version of the Ultimax, the Mk 4. This is a variant of the Ultimax 2000 version. Changes for the Marines include a MIL-STD-1913 rail atop the weapon, ability to use both the Singaporean magazines and US M-16 magazines (as well as those alternate magazines which will fit into an M-16, such as the C-Mag), an M-249/M-16-type flash suppressor, a buttstock which detachable and folding, a bipod which is folding and adjustable for cant and height, and uses selective fire (it may fire on semiautomatic, unlike the Ultimax 100 and Ultimax 2000). The Marines are testing both the 20-inch barrel and the 13.1-inch barrel versions, with an eye for using both, since the barrels may be easily interchanged. The future of this testing is as yet unknown, but the Marines are reportedly quite hopeful that the DoD will let them have the Ultimax 100 Mk 4.

Twilight 2000 Notes: This weapon was also used by the Israeli Defense Forces (in limited numbers) and by South Africa., but not Croatia. The Ultimax 100 Mk 4 does not exist in the Twilight 2000 timeline.

Merc 2000 Notes: As with many of Singapore’s weapons, the Ultimax is a mercenary favorite.