Machine gunners and snipers can "walk" rounds on target at long ranges with the optic.
The launch was the North's first this year.
It was not until the 1944 introduction of the P-51 Mustang that B-17s would be regularly accompanied by fighter escorts.
It could be the final package of military aid to Ukraine unless Congress approves supplemental funding legislation that is stalled on Capitol Hill.
By Lolita C. Baldor, AP
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