The U.S. has agreed to sell Taiwan 40 M109A7 155mm SP (self-propelled) howitzers. These will replace some, and eventually all the 146 M109A5s Taiwan received during the 1990s. Along with the M109s Taiwan will also receive twenty M992A2 ammunition resupply vehicles (each carrying about a hundred 155mm shells) and five M88A2 ARVs (armored recovery vehicle). These last two are built on the same chassis as the M109.
The M109A7 is a major upgrade and uses the same chassis as the M-2 Bradley infantry fighting vehicle plus a new engine control system. Added to that is the cab and gun mounts from the original M109. The A7 also has an automatic rammer, but not a more complex automatic loader. Crews will still have to manually load the propellant and 41 kg (90 pound) shell, but the semi-automatic rammer will then push the propellant and shell into the firing chamber and close the breech. Automating this part of the process improves accuracy somewhat, because when troops manually shoved (rammed) in the propellant and shell, they often applied too much, or too little, pressure and left the shell out of position by a tiny bit, just enough to hurt accuracy. The A7 also got new electronics, and numerous small improvements, many based on user suggestions. Not all the proposed upgrades were implemented immediately, but enough of them were to satisfy M109 users. The M109A7 made Paladin competitive with some new European self-propelled 155mm howitzers. The A7 is also heavier, at 35 tons and the new chassis can support up to 50 tons. Even at that weight, A7 is as fast as the existing M-109 and more maneuverable.
The M109A7 is also referred to as the M106A6 PIM (Paladin Integrated Management program). The first M109 entered service in 1963 and it proved so successful that it was ultimately adopted by most NATO countries and dozens of other nations as well. Including the many foreign license-built models, about 9,000 have been built so far. About a dozen nations still use it, often as improved models that were only used by the nation that developed a particular upgrade.
Taiwan is also getting 1,698 M1156 PGK fuzes that screw into the front of a 155mm shell, replacing the normal fuze that ignites the explosives when the shell hits something. A PGK fuze contains a GPS and small fins to guide the shell to a precision hit. The PGK turns a shell into a GPS guided shell that lands within 10 meters (32 feet) of the GPS location and is over 90 percent reliable. The PGK is not as accurate as Excalibur, the original GPS guided shell that appeared five years before and costs more than twice as much. Excalibur has the GPS guidance built in and can put the shell within three meters of the GPS coordinates. Both these shells are combat proven but the ability to turn any shell into a guided one and lower cost (about $15,000 each) meant the “cheaper but accurate enough” approach was more popular. PGK shells were heavily used in the effort to defeat ISIL (Islamic State in Iraq and the Levant) in Syria and Iraq. In Syria a single battery of six towed 155mm towed howitzers, operated by American marines, fired so many PGK shells that the barrels of two of their guns wore out. This happens when a howitzer fires a certain number of shells. Only six guns were used to support the U.S.-backed Kurdish forces that took Raqqa, the ISIL capital. This was done with low attacker casualties because missile- armed UAVs or 155mm guns firing PGK shells were always available to deliver precision firepower against ISIL gunmen who said they would fight to the death. Most did, but without much success in injuring their attackers. The marines sometimes used unguided shells, which was easy to do by just not installing the PGK fuze. With the PGK fuze the longer range (rocket assisted) 155mm shell is still accurate at its 48 kilometers max range as it is with the regular shell range, which has half the range of the rocket assisted one.
Taiwan also has to worry about a Chinese invasion using GPS jammers but that is a known problem and most GPS guided weapons are upgraded with jam-resistant GPS as well as less accurate but unjammable INS guidance.