Resurrected Weapons: AGM-136 Tacit Rainbow

A standard problem for a SEAD1 escort package is that if the enemy figures out what’s about to go down, they may shut off their SAM system radars, which makes it very hard to engage these radars. Switching off the radar has been as standard trick to spoil an antiradar2 missile (ARM) shot since the Vietnam War. Normally, one would expect SEAD aircraft to have to loiter over the target area, which is far from ideal. Loitering SEAD aircraft are vulnerable to fighters or short range IR guided missiles. An alternative concept was put forward in the ’80s with AGM-136.

AGM-136, which went by the unbearably dorky name ‘Tacit Rainbow’, was designed to provide an ARM that could loiter. Built on a cruise-missile type frame, it could be carried in the bomb bay of a B-52 or on the pylons of a wide variety of multirole fighter and strike aircraft. There was also a variant to be launched from the M270 MLRS. The idea was to use these reasonably low-observable platforms en masse against an enemy air defense network. If they found targets, they would seek out and destroy them like any other ARM. Otherwise, they could loiter in the target area waiting, making sure that the enemy did not switch on their SAM radars to engage the incoming strike package.

Like many advanced weapons of the late Cold War, the AGM-136 hit a number of cost overruns, because it had to fly in a preprogrammed area, recognize, and prioritize hostile radar emitters and then engage them. It was eventually cancelled in 1991. Advances in cheap microelectronics since the late 80s, plus the abundance of cheap GPS receivers, would make the AGM-136 a much easier development project today. It’s a nice supplement to EW aircraft like the EA-18G Growler, and would greatly help the survivability of strike packages while not requiring a correspondingly large investment in specialized platforms. With the increasing proliferation of higher-end air defense systems (even Iran has S-300s now), our strike packages will need all the help they can get. A platform like the AGM-136 is a great way to extend the survivability of non-stealthy platforms like the Viper or the Super Hornet.

The one thing that we’d like to investigate further is the ground-launched variant. In general, we would question whether the system would have enough fuel to fly from forward artillery positions to the target area and loiter while a strike package does its business. Near the front lines, we would not expect much in the way of powerful, long range air defense systems, simply because they would have to move quite a bit. On the other hand, they might prove to be cheap insurance over annoyingly potent short range systems like SA-15.

Verdict: Approved by Borgundy War Department Procurement Board, pending a rename.

1) Suppression of Enemy Air Defense
2) More often this is rendered Antiradiation missile, but I always thought Antiradar sounded better, and takes less explaining to the non-expert reader. Plus it’s easier to type.

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