Slitherine

I have an Italian fighter in Sicily but I can't make it attack the British fighter in Malta. A German fighter that I sent to Sicily on the other hand can. Is this a bug or am I missing something?

Air units may only be attacked once directly. If you attack something else say Malta, and the UK FTR is active it will intercept. Then you can attack it with the other air unit. If on sentry the air unit may only be attacked once.