Were aliens to turn up, we would have to fight them.

英訳に間違いが有れば正してください。

もしエイリアンたちが現れたら、我々は戦わなければならない。
Were aliens to turn up, we would have to fight them.

答え 間違いなし

If aliens were to turn upの接続詞ifを省略して倒置した文