The Pentagon has announced $1 billion in security assistance for Ukraine, the single largest package of weapons and equipment from its inventories since Russia’s February invasion.

The latest assistance package includes more ammunition for High Mobility Artillery Rocket Systems (HIMARS), 1,000 Javelin anti-tank missiles, artillery ammunition and 50 armored medical treatment vehicles, Under Secretary of Defense for Policy Colin Kahl told reporters on Monday.

Asked why HIMARS ammunition was included without additional systems, Kahl told reporters that the 16 HIMARS already sent by the Biden administration was “quite a lot” in terms of Pentagon assessments of Ukrainian territorial defense needs.

“Our assessment actually is that the Ukrainians are doing pretty well in terms of the numbers of systems, and really the priority right now is making sure that they have a steady stream of these GMLRS,” he said, referring to the Lockheed Martin precision munitions fired from both the HIMARS and the MLRS M270 family of launchers provided to Ukraine by British forces.

The new package also includes Claymore anti-personnel mines along with munitions for National Advanced Surface-to-Air Missile Systems, the same systems used to guard Washington, D.C.

The latest delivery of arms from the Defense Department brings the total amount of U.S. security aid to Ukraine to $9.8 billion since President Joe Biden took office last year, and $11.8 billion since Russia illegally annexed Crimea in 2014.

Kahl said Russia had seen heavy losses since the invasion of Ukraine began in February, estimating that Ukrainians had eliminated 3,000-4,000 Russian armored vehicles and inflicted 70,000-80,000 Russian military casualties.

Monday’s package announcement marks the 18th drawdown in weapons and equipment for Ukraine from the Department of Defense’s inventories. Pentagon officials have asserted the stockpile deductions will not hurt U.S. military readiness.