The jets are ready, and the flight instructors are waiting, at a new training center in Romania that was created to teach Ukraine’s pilots to fly the F-16 warplane. But there’s a catch: The Ukrainian pilots have yet to arrive, despite declarations last summer that the center would play a crucial role in getting them into the air to defend their country from increasingly deadly Russian strikes.

It’s still unclear when Ukrainian pilots will begin training at the center, at the Fetesti air base in southeast Romania, which NATO allies also are using to get schooled on the fighter jets. But the delay is a window into the confusion and chaos that has confronted the military alliance’s rush to supply the F-16s.

That is not to say that Ukraine’s pilots are not being prepared. Twelve pilots so far — fewer than a full squadron — are expected to be ready to fly F-16s in combat by this summer after 10 months of training in Denmark, Britain and the United States.

But by the time the pilots return to Ukraine, as few as six F-16s will have been delivered out of about 45 of the fighter jets that European allies have promised.

Nevertheless, their highly anticipated arrival over the battlefield will come not a moment too soon. Russia has employed more aggressive air support to gain ground in eastern Ukraine in recent weeks, using its warplanes to send guided glide bombs over long distances into the Ukrainian front lines.

And Ukraine is desperate for more weapons, of any kind, as it runs low on artillery rounds and other ammunition while Republicans in Congress hold up additional American military aid. The F-16s would likely come armed with short- and medium-range missiles and bombs, partially making up for the shortage of ground-based munitions.