Tacit Rainbow was a project to develop a jet-powered "mini" drone for finding and destroying enemy ground based radars. Designated AGM-136A by the Air Force, the Tacit Rainbow could be carried to target striking distance and air-launched by bombers or fighters, or launched from ground systems. Each vehicle was preprogrammed for a designated target area using the on-board computer and flight control system. Once launched, AGM-136A flew a preprogrammed course to its target area and "loitered" until it detected transmissions from an enemy radar. Once a radar source is detected and identified, the UAV homed in to destroy it. Unlike other anti-radiation missiles, Tacit Rainbow could not be "fooled" if the radar was turned off to avoid being hit. As long as fuel remained, it could wait and reattack that or another radar when operation resumed.
The Tacit Rainbow unmanned aerial vehicle (UAV) was conceived in the early 1980s using experience gained with anti-radar missiles in Vietnam. Its purpose was to supplement manned aircraft in striking enemy air defenses. The vehicle was designed for low cost production so that it could be used in "swarms" against dense enemy air defense networks.The Naval Research Advisory Committee (NRAC) 1989 Summer Study on "Defense Suppression in the Year 2000" recommended the development a family of decoys (that is inexpensive, realistic, modular, easy to carry onboard strike aircraft and carrier compatible, including a lethal version) for use in conjunction with strike operations to saturate the enemy IADS, and noted that Tacit Rainbow did not meet these requirements.
The first Tacit Rainbow air-launch occurred on July 30, 1984. More than 30 test launches were made, from both bombers and fighters. The MLRS launcher was also used for the Ground Launched Tacit Rainbow. On 21 March 1989 the Acting Secretary of the Air Force notified the Congress that the current program acquisition unit cost of the Tacit Rainbow program had increased by more than 15 percent, and on 23 May 1989 notification was provided that the Tacit Rainbow Program has exceeded its baseline unit cost by more than 15 percent.Procurement funding for the Tacit Rainbow missile was deferred by the Congress in October 1989, pending successful completion of operational testing. The next year's budget request for Fiscal Year 1991 contained $9.759 million to continue development of Tacit Rainbow anti-radiation cruise missile. The budget request also contained $227.4 million for procurement. Subsequently, the Air Force formally informed the Congress that an additional $27.0 million would be required in research and development funding because of delays in the program. The House authorized $26.759 million for research and development, endorsing the increase in funding requested by the Air Force. The House also provided $59.5 million for procurement, which was earmarked in the budget request for facilitating the factory of the follow-on competitor for the Tacit Rainbow program. The House restricted the obligation of the $59.5 million until the Secretary of the Air Force submitted a report evaluating the cost effectiveness of proceeding with two production contractors for the Tacit Rainbow program. The Senate authorized $36.759 million for research and development, and authorized the procurement funds as requested. The conferees recommend an authorization of $36.759 million for research and development and $59.5 million for advance procurement and agreed to the legislative provisions proposed by the House.
The ground-launched version of the nonnuclear TACIT RAINBOW ALCM had a design range of only 430 kilometers, and was therefore well below the newly agreed START threshold of 600 kilometer range for counting ALCMs.
Tacit Rainbow was a purely conventional system and there were no plans to equip it with nuclear warheads; therefore, the 1990 Strategic Arms Reduction Treaty [START] agreement did not have any effect on the US ability to employ it. The Soviet effort to capture Tacit Rainbow was part of their overall effort in START to try to constrain US conventional programs. The ALCM range issue in the START negotiations was a question of what range would mark the threshold between short-range systems not limited by START in any way and long-range nuclear ALCMs which would be covered by START. The US concern on ALCM range was above all to protect US conventional options. Since future non-nuclear ALCMs like Tacit Rainbow will not be limited by START if they are externally distinguishable from nuclear ALCMs, the US accepted the 600 kilometer range threshold in START. As a result of its tough negotiating on this provision, the United States gained concessions which eased the way for the deployment of new conventionally armed cruise missiles such as the highly accurate Tacit Rainbow. Secretary of State Baker agreed to constrain US military programs in a so-called `side letter' to the proposed START framework statement in which the United States agreed not to modernize the Tacit Rainbow ALCM, and also not to equip this ALCM with a nuclear warhead. This letter informed the Soviets of the fact that the US had no plans to convert the non-nuclear Tacit Rainbow ALCM to a nuclear ALCM.
In October 1990 Air Force investigators looking into mismangement at Northrop concluded that many of the expensive weapons systems built by that contractor -- including the B-2, the Tacit Rainbow anti-radar missile, the F-15's jamming system, the guidance system for the MX missile -- were riddled with fraud and performance defects. The program was cancelled for budget reasons in 1991, prior to the planned start of production in 1992. During the previous two decades, only two programs were cancelled after full scale testing had commenced and before a substantial amount of serial production: the Army's DIVAD gun (the Sergeant york), and the Tacit Rainbow missile.
Specifications | |
| Span | 5 ft. 2 in. |
| Length | 8 ft. 4 in. |
| Body diameter | 2 ft. 3 in. |
| Weight | 430 lbs. |
| Armament | WDU-30/B 40 lb. blast fragmentation warhead |
| Engine | Williams International F121 turbofan of 70 lbs. thrust |
| Cost | $200,000 (estimated production version) |
| Cruising speed | Subsonic |
| Range | air-launched = "More than 50 miles" ground-launched = 430 kilometers |