US officials announced that another $550 million in military aid would be sent to Ukraine, including 75,000 rounds of 155mm artillery ammunition and additional ammunition for High Mobility Artillery Missile Systems (HIMARS). Four more HIMARS, which have a longer range and are more accurate than older Soviet-era artillery rocket systems, arrived in Ukraine on Monday morning. “We have proven that we are smart operators of this weapon,” Ukrainian Defense Minister Oleksiy Reznikov tweeted on Monday morning. Ukrainian forces have used the weapon system to destroy at least 50 Russian ammunition depots since June, Reznikov previously said. CHILDREN TRAUMATED BY WAR IN UKRAINE FIND MENTORS FROM UNEXPECTED PLACES In late July, the Ukrainians used HIMARS to destroy the Antonovsky Bridge, a key crossing connecting Russian forces in the occupied Kherson region with the Crimean peninsula. FILE PHOTO: In this May 23, 2011 file photo, a launch truck fires the High Mobility Artillery Missile System (HIMARS) produced by Lockheed Martin during combat training in the high desert of the Yakima Training Center, Wash. (Tony Overman/The Olympian via AP) “[The Ukrainians are] spending a lot of time hitting targets like ammunition supplies, other logistical supplies, command and control,” a senior US military official told reporters last month. “All of these things have a direct impact on the ability to conduct operations on the front line. So I would say yes, even though they’re not firing HIMARS on the front line, they have a very, very significant effect on that.” CLICK HERE TO GET THE FOX NEWS APP The Biden administration has sent more than $8 billion in security aid to Ukraine since the Russian invasion, including Javelin anti-tank missiles, Stinger anti-aircraft missiles, drones and thousands of small arms. Reuters contributed to this report. Paul Best is a reporter for Fox News Digital. Story tips can be sent to [email protected] and on Twitter: @KincaidBest.