A spy plane has a transponder so you don't shoot a friendly/neutral aircraft down (or waste time classifying it as friendly/neutral.) The codes it squawks can

A spy plane has a transponder so you don't shoot a friendly/neutral aircraft down (or waste time classifying it as friendly/neutral.) The codes it squawks can be modified in various ways but there will be scenarios when you want your transponder, such as flying in an area where you have air superiority.