The U.S. is struggling to deliver effective systems that can counter the threat.

The Pentagon first said it would deliver a counter-drone system called Vampire in August, but did not approve a $40 million contract for the system until mid-December. The first four systems won't be delivered until mid-2023, with another 10 arriving by the end of the year, the WSJ wrote.

The Pentagon did not say why it took several months from the initial announcement before the contract for the anti-drone technology was awarded. The company behind Vampire said it was just paperwork.

It was just a process to find the right contract tool and the right mechanism, said Luke Savoie, president of intelligence, surveillance and reconnaissance at L3Harris Technologies Inc.

The contract underscores the complex efforts of the U.S. and its allies to help Kyiv counter the threat posed by the Iranian Shahed-136 drone. But it also underscores the difficulty of rapidly deploying systems in sufficient numbers to create an effective defense.

Although Ukrainian forces have had some success shooting down kamikaze drones or barraging munitions, no system has yet provided comprehensive protection.