The jets will bolster Ukraine's fighter fleet, which is still under fire from Russia's larger air force.
But air-defense ammunition is a more urgent need, one underscored in recently leaked US documents.
Berlin approved Warsaw's request to send jets to Ukraine on Thursday, the same day it was received.
Both air forces have shifted tactics and now operate farther from the front line, playing to the advantage of the Russian aircraft, which have an edge at longer ranges.
Without the threat posed by those interceptor missiles, Russian aircraft would have greater freedom to attack Ukrainian aircraft and bomb Ukrainian targets, including in support of Russian front-line troops, the leaked document says.