• An American weapon first dropped by stealth bombers over Kosovo in 1999 and then during combat in the post-9/11 wars will soon be used by Ukrainian pilots flying Russian-made jets to kill Russian soldiers.
• The weapon, called the Joint Direct Attack Munition, consists of a kit that turns a cheap unguided bomb into a highly accurate, GPS-guided weapon. It is usually referred to as JDAM. The Biden administration announced recently that the weapons would be part of a new $1.85 billion military aid package, giving Ukraine a precision-guided bombing capability it has never had.
• When dropped from higher altitudes, the bomb can travel about 15 miles to its target before exploding.
• With the right kind of equipment, Ukrainian jets could carry multiple JDAMs on a single mission, just like U.S. and NATO warplanes do.

What are these weapons?

• Technically speaking, JDAM refers to a kit that is bolted onto the U.S. military''s general purpose Mark-80-series bomb and turns it into a GPS-guided weapon.
• The Mark-80 warhead, which was developed soon after World War II, was designed to be easily fitted with a variety of tail fins and fuses for use in a range of situations. Over decades, different attachments have been fielded - for low-level bombing, and to turn them into land and sea mines, and finally into various types of guided weapons.
• It typically comes in three sizes ranging from 500 to 2,000 pounds. However, which model or models will be provided to Ukraine is unclear.
• Since their first combat use in the late 1990s, JDAMs have been improved and new capabilities have been added. They can work with a variety of fuses that control whether they explode above the ground, on the surface or after burrowing into the ground. One updated kit adds a pair of wings that open after the bomb is dropped, allowing it to fly more than 40 miles to a target.
• They are also relatively inexpensive, in the Pentagon''s math. A Navy fact sheet updated in 2021 put the basic JDAM kit''s average price at just over $24,000 apiece.

Where did they come from?

• JDAM was born out of the frustration that pilots and Air Force leaders had with a different kind of guided bomb during Operation Desert Storm in 1991.
• First used in small numbers toward the end of the Vietnam War, that bomb was called the Paveway II. At the time, the idea was considered revolutionary: An expensive kit fixed to the nose and tail of a Mark-80 could make the otherwise unguided bomb maneuverable along the path of a laser shone from the ground or from a plane above. But in Iraq, sandstorms and smoke often disrupted the path of the laser beams, causing the bomb to miss its target.
• Months after that war ended, the Air Force decided that military pilots needed a kit that would not cost more than Paveway II and could guide bombs in all weather conditions. A new constellation of GPS satellites offered a solution, continuously beaming radio signals that could guide bombs night and day, rain or shine.
• Air Force leaders accelerated work on a similar device to produce what ultimately became JDAMs, which are now made by Boeing at a factory in St. Charles, Missouri.

Why did the U.S. wait to give these bombs to Ukraine?

• Unlike some U.S.-provided weapons, the issue is not the length of training or the cost of maintenance. A few fundamental hardware and software problems had to be solved: JDAM kits were not designed to be used with Ukraine''s Russian-made bombs, and the country''s Russian warplanes cannot carry American-made bombs, nor can Russian flight computers communicate electronically with American guided munitions.
• Since Poland, a former satellite of the Soviet Union, joined NATO, some of its Russian MiG-29 warplanes have been converted to carry Western munitions, but that required replacing their Soviet-designed computer systems and some wiring with Western-made gear. A faster approach was needed for Ukraine.
• The Pentagon has said little about how it made that work.

What is the problem that needed to be solved?

• It took some MacGyvering, but the problem here was not unlike the one shown in the movie "Apollo 13," when NASA engineers had to fit different parts together in order to save the lives of astronauts in space - figuring out how to "put a square peg in a round hole," as the story went. This year, engineers had to essentially do that, and much more, to make JDAMs work on Russian jets with the minimal modifications.
• The standard bombs used by the United States and Russia are very different in design, as are the devices used to attach them to warplanes and drop them over targets.
• American-made bombs have two small steel lugs that secure them to racks designed to hold them snugly at high speeds and to quickly push them clear of the plane''s fuselage when a pilot presses a button to drop. By comparison, many Russian bombs have only one suspension lug, and the racks that drop them are incompatible with U.S.-made weapons.
• The U.S. military solved the hardest part of this problem months ago, when Ukrainian pilots first started shooting the American-made high-speed anti-radiation missile, or HARM. An adapter was created to connect a device called a pylon and other parts that hold the weapon to the jet.
• At Ramstein Air Base in Germany, a U.S. Air Force and Air National Guard team called Grey Wolf provides support to the Ukrainian air force, including on tactics and techniques, a military spokesperson said.

Is there more to it?

Yes, quite a bit.

• Carrying the bomb securely is one thing, but there are other problems. The electrical signal generated when a pilot presses the button to drop that bomb has to be converted to one that American-made devices recognize. And before being dropped, a JDAM needs data on the aircraft''s position and velocity as well as the target''s location fed into it electronically while the plane is in flight. Newer types of American bomb racks and pylons offer solutions. One "smart" pylon used with the HARM missile is now in service with Ukraine''s air force.
• The final piece is to transfer data from the cockpit to the pylon once all other conversions and adapters have been figured out, said Mike Pietrucha, a retired Air Force colonel who spent decades flying as a weapons officer on F-4G and F-15E fighters.
• More than a decade ago, he said, the U.S. military developed a system to adapt an American-made GPS-aided weapon on a foreign aircraft using a laptop with a GPS device that connected to the smart pylon via Bluetooth.
• "Today, the same function could probably be accomplished using a tablet with a GPS attachment, and perhaps commercial flight software," he added. "From there, the pylon would transfer the data to the bomb itself."

How many have been built?

• Boeing says on its website that it has made more than 500,000 JDAM kits for the United States and allied countries.
• How many are headed to Ukraine has not been made public, although it is likely that 500-pound JDAMs will be provided to start with. It marks a significant increase in Ukraine''s precision-guided munition capabilities.
• "It''s very important," said Andriy Zagorodnyuk, a former Ukrainian defense minister who advises the government.