KYIV, Ukraine – Ukrainian troops returned home from training in the United States and Germany three years ago adept at the standard way of using the Patriot system so critical to air defences. But with limited supplies and nonstop Russian barrages, they quickly realised they would need to rewrite the rules.So the Ukrainians started to experiment.For example, each battery, or firing unit, in the mobile surface-to-air Patriot defence system holds interceptors that are launched to stop ballistic missiles midair, before they crash onto the earth.The Ukrainians learnt to often fire just one interceptor at incoming ballistic missiles instead of the usual two or more because of shortages of the expensive American-made weapons.They also set the Patriots to manual mode to avoid automatic firing on