F-16s will pose as enemy aircraft to the newer F-35s and F-22s, Hansen said. But pilots will also be kept on their toes by nine electronic threat emitters — five from Volk Field and four being brought from other bases. They are devices with electronic signatures that match signals F-35s can pick up from enemy air defense installations with surface-to-air missiles.

The threat emitters can be moved on trailers and operated at airports — such as at Black River Falls and Marshfield — and other government facilities with microwave communications links.

“You never let them get used to where the threats are because in combat the threats are going to pop up where you least want them and where you least expect them,” Hansen said.

In some cases, aircraft simulate attacks on the supposed enemy positions, but more often they take evasive action, Hansen said. Threat emitters on Volk’s weapons range sometimes are augmented by inert projectiles that trail smoke behind them to look like an approaching missile, but usually pilots don’t find out until they return to base whether they acted quickly and effectively enough, Hansen said.