Persian Gulf state Bahrain is buying 30 M140 ATACMS (Army Tactical Missile Systems) artillery rockets from the United States. The UAE (United Arab Emirates), to the south, is buying 100 ATACMS rockets as well.
The UAE and Bahrain earlier purchased the M270 MLRS rocket launchers, which the ATACMS is launched from. Both countries are getting the ATACMS equipped with a 227 kg (500 pound) high explosive warhead. The U.S. used over 700 ATACMS in Iraq. These rockets use GPS guidance to hit targets up to 300 kilometers away. Sort of like the popular 500 pound JDAM smart bomb used by the air force, but not requiring an aircraft to deliver it.
When the U.S. Army first introduced its long range ATACMS rocket 24 years ago, it designed fancy warheads that distributed lots of smaller bomblets. While these worked, there was always a problem with some of the bomblets not self-destructing, and later going off when civilians, or American troops, came along. Not a popular weapon. Then, when a version, with GPS guidance and a single, 500 pound high explosive (or "unitary") warhead was introduced, it proved very popular. These rockets cost about a million dollars each. A 500 pound JDAM costs about $28,000, although you can add a few thousand dollars more to cover the expense of operating the jet bomber that delivered it.
The ATACMS is a 610mm rocket that fits in the same size container that normally holds six 227mm MLRS rockets. Although the army usually has enough air force bombers up there, carrying JDAMS, there are still times when a smart bomb is needed, and it's quicker to send an ATACMS, than to wait for the JDAM carrying bomber to arrive. ATACMS can also get through in situations where there are anti-aircraft defenses over the target area, keeping bombers away.
The primary military threat to Bahrain and UAE is Iran, but Bahrain and the UAE can only hit a small part of Iran with ATACMS. So the 130 ATACMS rockets are either for hitting Iranian forces that land on the western shore of the Persian Gulf, or at other neighbors who might, for some reason, attack. Saudi Arabia has sometimes had tense relations with its two smaller neighbors, but Iran is a much more likely, and hostile, neighbor.