Ground attack has increasingly become a task of converted trainers, like the BAE Systems Hawk or Aero L-39 Albatros, and many trainers are built with this task in mind, like the CASA C-101 or the Aermacchi MB-339. Such counter-insurgency aircraft are popular with air forces which cannot afford to purchase more expensive multirole aircraft, or don't wish to risk the few such aircraft they have on light ground attack missions. A proliferation of low intensity conflicts in the post-World War II era has also expanded need for these types of aircraft to conduct counter-insurgency and light ground attack operations.