As if one downed military aircraft wasn’t bad enough, the U.S. ended up losing two in the same day during its current war with Iran. The second plane hit by enemy fire on April 3, an A-10 Thunderbolt II, was in the middle of a search for the crew of the first plane, an Air Force F-15E, that was shot down earlier in the day. Fortunately, the pilot of the single-seat A-10 was rescued, but the aircraft itself is the latest casualty of the Iranian conflict. Considering just how much an A-10 costs, that’s not exactly a small loss for the United States. Even worse, there is only a finite supply of the A-10 Thunderbolt II, commonly known by its nickname, Warthog, because new ones aren’t being built anymore.

The A-10 Warthog originally rolled off the assembly line in the 1970s. At the time, the Air Force hoped to limit the cost of the plane to $15 million per unit when building the first 600 aircraft. That figure, however, is in 1970s money — today, it would be closer to $120 million for each A-10. The math gets even trickier when you consider that the Warthog that was hit over the Strait of Hormuz actually cost even more than that, because every A-10 currently in service has been upgraded over the years.

A big factor in the cost of the A-10 Thunderbolt II is its weaponry. Perhaps the most distinct feature of the Warthog is its massive 30-mm, 7-barrel Gatling gun, which makes up 16% of the plane’s total weight. Originally built by General Electric, the Warthog’s Gatling gun is now produced by General Dynamics and can fire over 3,900 rounds per minute or 65 rounds per second. Since it can fire depleted uranium, armor-piercing, and high-explosive/incendiary rounds so quickly, keeping the A-10 armed only adds to its cost.

Even more expensive, though, are all the upgrades and retrofits that the Warthog has undergone over the years, some of which even surpass the plane’s original cost. These upgrades include more powerful and advanced ordnance, such as precision-guided JDAMs, incendiary cluster bombs, AGM-65 and AIM-9 missiles, unguided and laser-guided rockets, and mine-dispensing munitions, among others. Newer defensive measures, like infrared countermeasure flares, electronic countermeasure chaff, jammer pods, and illumination flares, also add to the overall cost of the Warthog.

Major upgrades to the A-10 have been as recent as 2014, including more advanced communications systems, night vision systems, and a digital situational awareness pad in the cockpit. In just the past few years, Warthog pilots have started using pricey HObIT (Hybrid Optical-based Inertial Tracker) sights mounted on their helmets, which can target up to 6 to 18 targets simultaneously. One other expensive upgrade to the Warthog is a new pair of wings, which, on average, cost between $6.4 and $7 million each. These new wings were added to the remaining flying A-10s in the Air Force’s fleet. Around 162 of these Warthogs are still in service, and that number is only diminishing.

Besides its high cost, losing a Warthog in battle is a big deal because there are only so many to go around. The last A-10 Thunderbolt II was manufactured over four decades ago — way back in 1984. As previously mentioned, approximately 162 Warthogs (designated as A-10C since being upgraded) of the original 713 that were built remain flying. Despite the limited supply, the Air Force still has no definitive plans to replace the A-10.

Part of the reason is that, despite its age, the A-10 is still a very formidable aircraft. Thanks to all of its expensive upgrades, the incredible capabilities of the A-10 Warthog make it a significant component of America’s air power, which is very important in the current geopolitical climate. While it was originally designed and built as a countermeasure to powerful Soviet tanks, there are plenty of use cases for the heavily-armed, all-weather-capable, ground-attack aircraft/close air support (CAS) plane.

Eventually, no amount of upgrades will make up for its age, however. The U.S. Air Force has openly stated its desire to retire the aircraft and redirect its budget toward the more modern F-35 Lightning II. That hasn’t happened because, again, the A-10 is still a really, really good warplane. But, eventually, something will have to take its place, especially since — as the Warthog recently shot down by Iranian forces reminds us — there is a finite number of them.