Ukraine’s largest defense contractor has put up big bounties for Russian aircraft, payable to the pilots that fly them. Ukroboronprom, a state company based in Kyiv, has promised to pay up to $1 million in U.S. dollars for fighter jets and $500,000 for helicopters. In the past, various governments have tried to use the allure of fast cash to bait pilots to switch sides during a conflict—a tempting offer for pilots who don’t make much money, and may not agree with their government’s policies. But that history is dotted with mixed results.