The Special Purpose Individual Weapon (SPIW) was a long-running US Army program to develop a workable flechette based "rifle". Developed primarily by Irwin Barr, one of the founders of AAI (Aircraft Armaments Inc.), the program developed weapons over a 15 year period but was never adopted. The concept was revived in the 1980s as a part of the Future Rifle Program and again in the 90s under the Advanced Combat Rifle program, but neither program resulted in a system useful enough to warrant replacing the current M16.

Project SALVO

The idea of a flechette-based individual weapon started in earnest during the Army's Project SALVO. SALVO had earlier concluded that a small weapon with a high rate of fire would be considerably deadlier than the large "full power" weapons being developed in the 1950s, and followed several lines of investigation to find the best solution. SALVO had a small number of "duplex load" weapons developed, where two bullets were stacked, while Springfield and Winchester both entered multi-barrel weapons.

Even before the SALVO tests, Barr had been developing single and multiple flechette cartridges. The Navy became sufficiently interested in the concept to provide him with some development funding from the Office of Naval Research, resulting in a 12 gauge shotgun shell firing 32 flechettes. The Army later added funding as well, and AAI was invited to SALVO. In SALVO testing they were found to be able to penetrate one side of a standard steel helmet at 500 yards --excellent given their light weight-- but the dispersion of the darts was so great as to make them not very useful.

Further development continued by adapting a Winchester Model 70 rifle with new XM110 5.6x53mm rounds firing a single dart. The result was a weapon with somewhat less accuracy than the 7.62mm NATO rounds, but with equal penetration and a trajectory so flat it could be fired with no sights out to 400 yards. Better yet the rounds were very light, and had almost no recoil in comparison to even the .22 caliber weapons under development. This meant they could be fired at extremely high rates of fire, from a very lightweight weapon.

Since the Army was by this time only interested in fully-automatic weapons, Barr suggested that they build a multi-barrelled prototype in order to quickly test the concept. The resulting "burst simulators" were tested in 1961, and the general conclusion was that the light weight of the flechette meant that it could be fired at extremely high rates of fire, the baseline being 2300 rpm, from a weapon of only 3.5 pounds, fully loaded with 60 rounds. Needless to say, the Army became terribly interested.

Project NIBLICK

Meanwhile the Army's Operations Research Office, ORO, had been working on Project NIBLICK, follow-on to SALVO to develop a modern grenade launcher. Interested in the original shotgun-type shells, they recommended development of a dedicated flechette-firing weapon combined with a grenade launcher, the SPIW. The final requirements resulted in an over-under weapon, firing flechettes from one barrel, and grenades from the other. It was to weigh under 10 pounds fully loaded with three grenades and 60 flechettes.

Four companies responded to the contract tender, AAI of course, Springfield Armory, Winchester Arms and Harrington & Richardson. AAI continued with the original 5.6x53mm XM110 rounds, while Springfield and Winchester used a new 5.6x44mm XM144 cartridge. The H&R design loaded the dart from the XM144 into their own cartridge design.

The H&R design was the most advanced. It mounted the dart between three plastic sabots in a triangular plastic cartridge. When fired, the sabots were discarded early in small "sub-barrels" while the dart continued down the main barrel. Although the rounds were lightweight the weapon itself was not, at 24 pounds loaded, and the weapon was quickly eliminated from the contest.

Winchester's design used a "soft recoil" stock which absorbed the recoil of an individual round in a spring. The idea was to allow three rounds to be fired before the spring was completely compressed, meaning that there was no recoil at all until the end of the burst. This was intended to dramatically increase the accuracy of burst fire, but the system never truly worked right, and was later dropped. The grenade launcher portion of the design proved much more interesting, however, and work continued on that portion.

The Springfield entry was most interesting for its layout. It used two 30-round magazines back-to-back in a bullpup layout, taking rounds from the front magazine first. However their massive magazine-fed grenade lancher pushed the weight to 14 pounds, and it seemed unlikely this could be reduced by much.

Oddly, AAI's design was the least technically advanced. The rifle portion was somewhat heavy, but fired at 2400 rpm. Their grenade launcher was a simple single-shot weapon; their semi-automatic version was not ready in time for testing.

The conclusion of the testing was that none of the weapons was ready for development into a combat system. The AAI rifle portion and the Winchester grenade launcher were both interesting for general development however. More worrying was the results of general testing of the flechette concept. While the weapons delivered on their promise of extremely high rates of fire and excellent penetration, the rounds themselves were extremely expensive to produce, and the darts could be easily deflected in flight even by heavy rain. Finally the rounds gave off extremely loud reports and had a huge muzzle flash, making the guns easily visible in low-light.

A second round of testing followed, with the Springfield model adopting the Winchester grenade launcher with a disposable magazine and a new side-by-side layout for the flechette magazines. AAI's design was equipped with their semi-automatic launcher, which was now complete, and a new plastic buttstock/sighting system. Neither updated version proved very reliable and both were over the 10 pound limit. In 1966 SPIW was put into "maintenance mode" and the M16 adopted.

AAI continued development at a low level, and eventually managed to dramatically improve the reliability of their XM19. However this revealed another problem, that heat buildup in the chamber was great enough to result in "cook off". Changes in the Army command structure and the adoption of the M16 made interest in the SPIW fade, and eventually the project was allowed to die. Ironically AAI's original "simple" grenade launcher turned out to be a major success, when it was selected as the M203 in 1968 and became a common weapon under the M16.

The Future Rifle Program

But the concept simply refused to die. In 1969 the Army started the Future Rifle Program, and invited AAI to enter against General Electric's version of the older Springfield design (Springfield had closed in 1967). Additional entries with multiple flechettes or bullets ("micro-caliber") were also entered, mirroring the original SALVO tests of the 1950s. However the program came under attack by Congress as a waste of money, and was forcibly scaled back. Testing finally began in 1974, and the AAI design never managed to fire more than 6 bursts before jamming.

Close-Assault Weapon System (CAWS)

It was revived again during the semi-automatic shotgun-like Close-Assault Weapon System (CAWS) project in the early-80s. A number of designs were entered and offered fairly good reliability, but the entire concept of a large weapon for use out to 100 yards was questioned and the project later dropped.

Advanced Combat Rifle (ACR)

... and again during the Advanced Combat Rifle (ACR) trials in the mid-90s. Several designs were entered, from the simple Colt ACR to the more interesting flechette designs. Although the basic problem of a single-dart flechette round was finally solved by this point in time, none of the weapons entered offered the 100% improvement over the M16 that the Army tests required.

Modern Variants

Since the demise of the SPIW, there has been another attempt to revolutionize the assault rifle by way of a small projectile and a very high rate of fire, namely the HK G11. That project has not resulted in a production rifle either.