The US Army also wanted a 40mm Bofors replacement and towards the end of the 1950s a new gun and cartridge were developed to meet this need. They chose a calibre which they had traditionally used, 37mm, but a new 37 x 219SR T68 cartridge was developed, featuring a shell with a long, tapered ballistic cap or windshield. The cartridge case is based on the 40 mm Bofors case, shortened, necked and with the rim turned down. Early Vigilante cases even retained the 40mm Bofors' clip groove in the base. The mouth, neck and shoulder of the case were the same as the 37mm M16 and 37mm M17 cases for the U.S. anti tank and anti aircraft weapons, respectively, except the neck was shortened so the cartridge could have a similar overall length while employing a projectile with the rotating band farther to the rear. Standing next to each other, the Vigilante ammo and the anti-tank round have similar overall length, and nearly identical placement of the shoulder and the same shoulder angle, the only real difference is the shorter neck and wider base of the vigilante round. Muzzle velocity of the T68m was 915 m/s, but the shell weight is not given. This photo shows the Vigilante cartridge (right) next to the 35x228 Oerlikon round. The gun was also different; the biggest of the rotary cannon. In general principle rotary guns are similar to revolvers in that they have multiple chambers to speed up reloading, except that each chamber has its own barrel and the whole lot spin round under external power. The gun was designated T250, had six barrels and was fired at 3,000 rpm (reduced to 120 rpm for engaging ground targets). The gun was fitted to a tracked carrier, the T249, based on lengthened version of the chassis of the M113 APC. The gun is shown below, with another view showing its 192-round pan magazine on the left side of the turret. Vigilante had reached the evaluation stage in 1960 but was cancelled shortly thereafter. Its development was overtaken by a precocious new American missile system called Mauler, which was intended to operate automatically once switched on. It was supposed to detect threats, fire a missile and guided it to its target without human intervention, leaving the operators (in Ian Hogg's words) to chalk up the score. Like many ambitious early missile projects, this promised far more than it was able to deliver and was eventually cancelled in 1965, but not before it had terminated the Vigilante. The US Army was left with the M163, a 20mm Vulcan rotary mounted on a M113 tracked vehicle. One last postscript to the Vigilante story: Sperry brought the gun back out for one last try during the US Army's DIVAD competition of the late 1970s. Their unsuccessful entry used the Vigilante rechambered for 35 x 228 Oerlikon, mounted on an M-48 chassis. For a detailed description of the genesis, progress and outcome of the DIVAD competition, see THIS account. Any other information about the Red King, Red Queen or Vigilante will be gratefully received.