The necessary weapons were accumulated over several months.

For months, the administration of US President Joe Biden has been supplying weapons to Ukraine for a major counteroffensive to liberate the southern regions from Russian invaders.
CNN writes about this with reference to a representative of the White House.
An unnamed official said that Ukraine was asking the United States for weapons designed specifically for a counteroffensive in the south. The US complied with these requests, in particular for the supply of additional ammunition, artillery and Javelins. The deliveries took place as part of several US aid packages over the past two months.
“These packages were common knowledge, but it was not known at the time that they were designed in part to support the counter-offensive that is now underway,” the newspaper writes.
US Secretary of Defense Lloyd Austin and General Mark Milley have been in regular contact with their Ukrainian counterparts to identify specific weapons for targets in the south.
As UNIAN reported earlier, on August 29, the command of the Armed Forces of Ukraine reported that a counteroffensive of our servicemen had begun in the Kherson region . The Ukrainian army urged not to hurry with statements regarding the actions of the defenders of Ukraine in the Kherson region.
On the same day, CNN reported that in the southern direction, not far from the occupied Kherson, fighters of the Armed Forces of Ukraine had liberated four villages from Russian invaders .
(C)UNIAN 2022

Good job, Washington. It’s just too bad that the large European powers are so disgustingly hesitant to help Ukraine. After all, this war is at THEIR doorsteps.
Dmitry PissKopf IS ‘SAFE’ in Nikolaev.
Hahaha, Sir Veth, you used the Russian spelling of Mykolaiv 😉
I’m really glad Joe is safe, I wonder how many Moskali he killed?