The Defense Department announced today an additional $1 billion in security assistance to Ukraine, which will include Harpoon coastal defense systems, more 155mm howitzers, and more ammunition for the High Mobility Artillery Rocket System, or HIMARS.
The latest tranche of security assistance bound for Ukraine was announced earlier today by Secretary of Defense Lloyd J. Austin III and Chairman of the Joint Chiefs of Staff Gen. Mark A. Milley, who are both participating in the third meeting of the Ukraine Defense Contact Group in Brussels.
Senior defense officials later discussed the announcement in more detail during a background briefing at the Pentagon.
"The United States will be providing Ukraine with another $1 billion of security assistance," an official said. "This new assistance will support Ukraine's most urgent needs for artillery, as well as near-term priorities for coastal defense, secure communications and optics."
This latest package of security assistance come in two forms. First is a presidential drawdown authority, or PDA.
A "drawdown," according to documentation available from the Defense Security Cooperation Agency, allows the president in certain circumstances to withdraw existing weapons, ammunitions and material from existing U.S. military stocks and provide that to other nations. 
According to a fact sheet published on the Defense Department website, about $350 million of the $1 billion announced comes from presidential drawdown authority. This drawdown, the twelfth of its kind so far, includes 18 155mm howitzers, 36,000 rounds of 155mm ammunition, 18 tactical vehicles, additional ammunition for High Mobility Artillery Rocket Systems, four additional tactical vehicles and spare parts and other equipment.
The remainder of the $1 billion support comes from the Ukraine Security Assistance Initiative, or USAI. One defense official said this is an authority the department has been using to support Ukraine since 2015, when Russia first invaded Crimea and Eastern Ukraine.
Support under USAI differs from that provided as part of PDA in that it must be purchased or contracted rather than being pulled from existing military inventory, the official said.
"It enables the department to make direct purchases of equipment as well as contract for training and maintenance and sustainment, including in support of equipment provided through presidential drawdown,” the official said. "The USAI programs, in addition to meeting Ukraine's shorter-term needs, also help ensure Ukraine's enduring strength by providing for procurement and training of Ukrainian forces on NATO standard equipment."
Of the $1 billion announced, $650 million is made up of USAI. This includes two Harpoon coastal defense systems; thousands of secure radios; thousands of night vision devices, thermal sights and other optics. It also includes funding for training, maintenance, sustainment, transportation and administrative costs.
"The provision of [the] Harpoon is not in response to any particular piece of new information," the official said. "It's a combination of continued consultation with the Ukrainians, and coastal defense still being near the top of their urgent requirements list."
Since the beginning of the Russian invasion of Ukraine, Feb. 24, the U.S. has provided approximately $5.6 billion in security assistance support.